You are an dishonest time-traveler from the year 3100. You would like to travel back to our present day, and with your advanced technology, convince us that you are a god. You have unlimited energy, nigh-magical future tech, and few morals. How would you make most of the industrial, fairly educated people of today's world believe that you are a deity rather than a fraud or time traveling swindler?
First, start a religion. This should be pretty trivial - you just need a few miracles that aren't currently explainable. Now you have some followers.
Implant nanotech into your followers (or possibly just everyone?) that reads and records their mind. When they die, create a simulacrum of their existence that thinks and acts like they do. Put this into your version of the afterlife, which in reality is a massive VR server running that gives all your simulacrums, for the most part, whatever they want.
Now here's the kicker: You can let people visit it before they die.
You will need to dress things up to be all mystical and holy-like, but have a setup that will take one of your current/potential followers and let them visit the afterlife. They can literally talk to people who have moved on and received their heavenly reward. Rather than being a nebulous, unknowable heaven, you offer real, demonstrably, provable immortality.
As a side bonus, since you have nanotech reading the brains of everyone you can data-mine them for useful information - the ultimate in insider trading and intelligence.
Note: You probably don't want people to have to die before you can use this tactic, so you could create fake NPCs from a certain period of history. For example you could pick a "dead" religion and pretend that's you. That way you don't have to worry about simulating people who died before you can read them, but who your followers might still have known (parents/grandparents, and the like).
Here is the plan:
First, incarnate not as a god, but a prophet. Gather a bunch of followers (seems not too difficult, considering your powers). Then make a very detailed prophecy of things to come (and to be acted out by yourself).
What does happen when somebody claims to be prophet/ psychic/ 'the new shit' and has not got the weapons/ political power/ historical justification, like some contemporary organizations? The skeptics show up. Get invited by James Randi / Richard Dawkins etc. for a SMALL show of abilities which from today's viewpoint, are impossible (levitate, faith healing of broken arm etc.). Let them examine this closely. Let the media spread your fame. Then you can levitate into space, recorded by dozens of amateur and professional filmers, but not before you hold a speech to the masses, about the coming of the deity in the year ____. This date can be anything from 1/2 year to 50 years later.
In the year ____, you literally descended onto earth from space, act like you 'predicted' earlier, this time you will not need to hold back with your abilities.
A kind of mission statement (the mission can then be fulfilled) would be useful too. Something along the lines ' I've come to exterminate every racoon on earth, as they are truly a source of elemental evil...'
EDIT / FURTHER thoughts: From your question:
You have unlimited energy, nigh-magical future tech
It depends on the 'nigh-magical' but what exactly is the observable difference from 'unlimited energy' to a deity?
I will not cite this worn out phrase, but it does apply here.
In short: If you have (near) omnipotence, is it wrong to call yourself divine?
The difficulty in this question is not convincing people you are a god. You don't need to try to do that, just exist and some kooks will start thinking that. The difficulty is in trying to get 'most people' to believe the same thing. Now, in the modern liberal tolerant world, that is hard - no sooner when some people start believing, would lots of people start believing the opposite to just oppose the first group. Most people's default response would be to not give a damn.
So you basically need to get up in their face, and roll back the clock on the world to a time when people could be mostly homogeneous in their beliefs.
Step 1: Control the flow of information.
Let's say you brought back a nice little computer that could break RSA encryption, and a very clever and complicated little virus. Bam, the internet is yours. Start to subtly isolate and filter content. You don't want any way for opposition to organise against you. When people see you on the news and google 'is this dude for real', they'll see only what you want them to see.
Step 2: Be impossible to ignore.
Large scale international miracles are the best. It'll depend on what you have available, of course. Can you draw text to every person on the planet's retinas simultaneously? Can you make people unable to sleep until they make a personal verbal statement of their belief in you? Can you write your name on the moon, or the surface of the sun?
Step 3: Discredit the opposition.
Obviously step 1 is not going to be perfect. So you are going to have to make steps so that the vast majority of people hate, hate, haaate whatever opposition manages to organise themselves against you. You can do this with guilt by association (this bad bad guy disbelieves, are you sure these disbelievers aren't bad either?) or by producing false flag attacks. You might even take a page from 1984 and generate your own opposition. Like have a cult be created that still thing you are a diety, but an evil diety. That would help change the terms of any opposition into a win-win situation, and make your enemies easier to monitor and easily to disparage.
Also, these days, it's better for a would-be god to never physically appear. Then there's no one for them to want to kill or hate, just a concept or a voice that you control from behind the curtain. If you are vague enough, a lot of religious people can be made to convince themselves they already believe in you.
Just use your super crazy tech to do some "miracles" and claim to be a god, perhaps choose a god in particular and make everyone think you are it (make others call you Zeus, fornicate with anything that moves and electrify to death anyone looking at you funny).
Demand people to do your bidding and offerings or they explode, and give some benefits to those that do as told. Make sure to make examples of those who would deny your godhood.
If someone is allowed near, make sure you have some sort of force field in case of sneak attacks and make sure to check for any kind of poisons. After a while those who would try to kill you would see the futility and accept you as some sort of god, if only for how hard it is to kill you.
Who Doesn't Love a Second Coming?
You've got a time machine, and people a few thousand years ago may have been a lot easier to convince than they are now. Go back to some arbitrary time and show off some miraculous behavior.
Build up an opposition (this part is important), and rally your troops against them. Introduce a vaccine to your true believers through a ritual of some sort shortly before some climactic conflict, then unleash a biological plague on your enemies, so when your side wakes up, they find the opposition decimated and winning seems miraculous.
Have monuments made to you. Introduce stone-cutting techniques that the natives couldn't possibly have and more importantly couldn't replicate. Make them sacred so that no one would ever write about them (better yet, pick a culture that hasn't developed writing), and take them with you when you 'ascend to the heavens' or travel to the current day.
Have a sacred cave that belongs to you, and have it packed with items that describe geometric principals or crop rotation or other things mankind didn't discover for 1000 years. Have extremely accurate drawings and carvings of you included. Make sure none of it has intrinsic value like gold or jade. Have it sealed and cursed. Lay traps for thieves. Ensure that it is in a location that won't be discovered for 1000 years. Or perhaps in some particular natural disaster.
Predict the exact time and day and circumstances of your return. Have it be just after a huge natural disaster, and perform something that could even be called miraculous in today's jaded environment. Make sure that it is coincidentally televised, and make sure that you save a lot of people in the process.
There will be very vocal skeptics. They will say, "If he is god X, why hasn't he done Y?" This is where your cave comes into play. If they come up with something you didn't think about, go back and put proof of Y in the cave. Never respond to the skeptics directly. Keep all of your public acts positive. Feed the world, introduce cheap desalinization, save the world. Go back to when your inconveniently vocal detractors were kids, and kill them in some sort of accident. Being as unscrupulous as you are, who cares about the consequences to the future time-line?
The thing about the scientific method is that even with scientists, it is very hard to convince them of something when the overwhelming anecdotal evidence points the other way. There will be people strongly opposed to the prevailing belief in you, but deep in people's hearts, they will be unconvinced by any argument when your divinity is so obvious.
Now, I'm not saying you should go for an Almighty figure, or claim to be Jesus or something. Be a pantheon god, because they were fallible. This is much easier to pull off. Of course, you'd be asked to explain why any of the other gods haven't returned, but like I said, never address such questions. Let your acts speak for you. Be aloof. Or be someone more enigmatic. Without doing the research and just going by memory, it seems that Quetzalcoatl might be easy to co-opt.
Gusk has an easy way to do it, but you don't have to go that far.
People want to believe, which is why there are so many cults out there.
The guy in Waco had his followers convinced that he was Jesus returned, and he didn't have any special powers or abilities.
Smiting people could help establish his power, but it would also cause rebellion against him, especially with all the skeptics around. Eventually someone would get a lucky shot in and he'd be a dead god.
Best to leave the smiting as a last resort and just show off some power. Stay mysterious.
Between now and 3100 there will probably be a few cults, just steal from their playbooks, and he'll start to pick up followers. Stop a natural disasters... You'll never get 100% of the people. The idea is to pick up enough to have some political power and money.
Use the same ways most people are convinced of godhood.
Prophecy You're a time-traveller. Download some history off the interwebs and, occasionally, start speaking in tongues and, afterwards, divulge information on some event or other. Keep it mysterious enough that no one can act on it... For example, Germanwings flight 9525 could be "A guardian betrays! A flight, the earth reclaims!" When someone asks why you cannot be more specific, say that "It is not for you to question. Be satisfied, or begone." Of course you might accidentally change history
Cure the Sick This is a big one. People will often do a lot to cure their own illness, or a loved one's. Bring some cancer-fighting drugs and slip it into someone's food before the great magic act. If you cure someone's hopeless illness, you've probably got a follower.
Perform Miscellaneous Miracles Find a good spot to dig a well with some 32nd-century scanner. Create loud booming noises with a stealthy drone. Point at a tree and watch as it erupts in flame (due to energy projection from said drone). Separate salt water into salt and water. Create a YouTube post that only gets intelligent comments.
You don't have to convince everybody. Sure, some people will see your claim and laugh. But anybody who says you're a time-travelling charlatan from the year 3100 is going to generate just as many giggles.
No need to convince them...
If you're dishonest enough, you also may be disrespectful enough to override the annoying glitch called "free will".
With your "indistinguishable from magic" technology, reprogram your target organisms' neural circuitry to worship you as a god.
They will be your loyal subjects no matter how illogical it is to do so.
Bring lots of tech. Tech that doesn't look like tech. Mostly nanomachines, as they can be renewable. Do lots of pointing at things, and making those things do stuff without you appearing to physically touch them at all. Turn on lights, open knob-handled doors, make plants wilt, smite naysayers. That kind of thing. Stuff we don't yet have the tech to do. It will be very easy to convince the fairly educated gullible, and there are lots and lots of gullible. It is VERY easy to persuade someone away from religion; you presently work miracles, and other gods are not around to defend themselves.
Convince everyone personally.
You don't have to do this in person yourself, of course: that's what your army of AI-controlled clones is for‡. Every person on the planet can have a personal conversation with You As God, and every clone of you will be able to perform miracles sufficient to persuade whoever it's currently talking to. Said miracles may include smiting, seduction, using the water/wine miracle to get drunk with someone, creating a golden statue from nothing, or a simple conversation about philosophy.
You don't even need to be consistent. Even if all of the mortals start comparing notes about you, it doesn't matter: they'll be persuaded that you're a god, even if you say completely contradictory things to different people – you'll just be an inconsistent god. And if various people manage to convince themselves later that you're a hallucination/con-man/alien, just have another clone drop by with further proof of your divinity. You'll end up with a few people who are stark raving mad and/or cripplingly paranoid, but as long as most of the planet is convinced that you're a god, surely that's good enough?
The important part here is to make sure that nobody can ignore you. On a personal note, there are plenty of things I've filed as "that's weird, but ultimately irrelevant to me; it could be a god or simply something we don't know enough about yet." But if you're visiting people in person, repeatedly, with nigh-indisputable "miracles," then they can't just dismiss you as irrelevant.
‡: The AI is, of course, both immensely powerful and friendly to you, and will do what you intend, rather than merely what you ask for. All of that silly "rebellious AI" nonsense got taken care of in the Great Reprogramming in the year 2934.
Fake someone else's second coming
Hello, I am...
- The Buddha.
- Pick a Hindu God.
- Steve. Remember before I died, I said I'd be back? It's documented. I am God.
- The Prophet. I was prophesying myself.
- Hercules, Achilles, some son of the gods. I've been hanging out in constellation form.
- Grandpa. I discovered Immortality. Back from the afterlife.
- Ozymandias, the pharaoh, child of the gods, now in god form. As predicted.
- A dead pop star. Some people already thought I was God.
In the present day, it's probably going to be a lot harder to convince people than you might think. After all you, a person in the present day, are considering time travel and highly advanced science as a way of faking being a deity. So what's stopping someone else from doing the exact same thing as an explanation?
It isn't just our understanding of science, but our fiction that makes people less inclined to immediately jump to the deity explanation.