- this happens within a relatively isolated region. Perhaps a country, perhaps some city state. Point is, it's not some all reaching, omni-present government.
- the telepaths have finite manpower, time, and ability to scan everybody. So, it's possible for them to miss somebody. They aren't like professor X in Cerebro apparently able to reach everybody on the entire Earth.
Basically, it boils down to - you could evade the telepaths. What you do then is...evade the telepaths. It's not going to be easy all the time - even a small gathering of people could be detected. If Alice and Bob are absent and the telepaths scan Mallory's mind and find out they keep gathering in her basement all the time and from scanning Eve's mind they find out Alice and Bob have been talking about avoiding the telepath patrols. That's probably suspicious enough. And a resourceful/determined enough telepaths might be able to dig out that information.
So, a good solution is to avoid being suspicious. If Alice and Bob (and the rest of the resistance forces) stay around the patrols enough, they keep risking being found out directly or indirectly from other people knowing of their actions.
As stated, my assumption is that these can be avoided. Maybe the patrols are more lax in certain cities, maybe there is another country that telepaths don't have (easy) reach to, perhaps it's as "simple" as running away to the not-very-hospitable forest up the mountain. Still, if it's possible to get away from where the telepaths and their patrols are, then Alice could arrange going there. Could be posed as a business trip, or a sick relative or whatever that might make it sound feasible to others that Alice would leave at a time when the telepaths might not be around. And this is important, because the goal here is to avoid being "interrogated" by a telepath (who might easily find Alice is trying to flee) as well as to mislead others that she's not doing that. The telepaths probably would have wanted to do a scan and then let her go, but with Alice gone, they could just do a sweep of all her close relatives and acquaintances. If none of them appear to know anything but the story of her having to leave in a hurry, then the telepaths might be satisfied.
Perhaps there already is resistance outside the grasp of the telepaths, perhaps one has to be established yet. At any rate, the goal is to get people away. Once there, they can really start planning without having constant literal thought police around. Alice can now start planning and shipping out close individuals.
A sufficiently organised resistance might be able to do a lot more. For example, they could smuggle people into the city via tunnels. They might also be able to fake deaths of people to smuggle them out. Some sort of concoction might make a person appear dead enough to fool relatives (for a cover story) and maybe even telepaths (no mind to scan). The "dead" person would then be shipped to the resistance. With some resourcefulness, a false epidemic hoax could be spread to justify the unusual rate of otherwise healthy individuals dying lately.
At any rate, these are just ideas - again, point is, the resistance would be operating outside where the telepaths could catch them and the first goal is recruitment, while keeping low profile.
The next goal is training. The specifics might depend on the exact abilities of the telepaths but some sort of mind protection might be in line but also ways to actually take them down. If there is no protection possible to allow a person to at least approach a telepath for a kill (let's assume an attempt on their life from within 20-50m away), then the training could be in traps, poisons and maybe long range shooting. The resistance have to find what the safe approach to the telepaths is and how to kill them.
An alternative here is a way to somehow disable them but all in all, doesn't change the basic premise or basic tactics. Whether killed or non-lethally taken out, it is really the same thing in terms of story.
So, after training, comes organisation. The telepaths have a strong hold and taking them one by one is only going to make the rest tighten their hold on the population. So, one decisive action should be taken against them. This could be bombing them, or filling their evil telepath tower with gas that takes out mental powers. Whatever it is, it's not going to neutralize all, but it should at least cripple their manpower. And this action might be against a single city, rather than everywhere the telepaths are. It really depends on what location is of good strategic value. It might be the capital, it might be a key city that cuts supplies to another part of the county. So, that needs to be carefully planned and prepared for. Some supplies (bombs, gas, weapons) would need to be smuggled into places, positions need to be found, the resistance forces need to be trained.
Next step, spring the trap and break the telepath's hold. One way this could go is try to simultaneously (or in short succession) take out the active telepath patrols. Or maybe bomb their HQ. Whatever makes more sense but it would disrupt them - no patrols leaves the telepaths without information of what's happening in the city, no HQ might lead to nobody collating and organising the information from the city. The chaos from the first attack should then be used to launch an immediate offensive against the rest of the telepaths. With no HQ, the telepath patrols are very vulnerable - if surrounded, they would know people are out to get them, but can't really do much. If there is a lot of panic in the streets, the patrols might even be overwhelmed with information. If the patrols are take out, then the resistance has an easier movement through the streets. Other telepath patrols might still roam, but would need to get to the affected areas first and the resistance could still use the time. They could:
- approach HQ and start an attack. Say, vent gas into it or set off charges.
- arm the population and wait for the telepath forces to come in, then attack them. The forces might not even be consisting of telepaths - police or the army could be dispatched, in which case, they wouldn't necessarily know who is enemy or not. A telepath would also have a hard time - walking into a neighbourhood and finding two hundred minds who want to kill you would not generally help. The above mentioned chaos could also mean telepaths are not very useful.
- move in and take out the rest of the telepath patrols.
The resistance could do all these and even more than one at a time. Or other things. In the ideal case, the resistance provides the spark for a revolution, but even if they just take some significant number of telepaths, that's going to work. The telepaths would have their mind scanning abilities stretched thin.
Still, let's talk ideal scenario: the resistance manages to overthrow the telepath control in the current area. This is probably something like a city. The resistance inspires and pushes other people to join into the warfare feeding the resistance's ranks. All this is done in a relatively short time - maybe a day or two, maybe an hour or two. After liberating one city, they use that as a jumping off point to liberate other ones. In some respects, a second easy would be harder, because the telepaths would not be caught by surprise, in other respects it would be easier, because the resistance would have more people in its ranks. Mind reading is better at preventing a rebellion before it starts but it's not very good with one currently at work. It only tells you the obvious - that the people with weapons and an angry frown want to kill you. It could give you some tactical information, like that they are behind the wall or where their HQ is, but that also depends on how that power works. Here I'm assuming that it takes some time - a telepath can't get all the secrets of the resistance with a glance and in active combat their abilities are limited to knowing slightly more than the obvious.
With more cities liberated, word should now start spreading. Which could be the final nail in the coffin for the telepaths. They would either have to announce that "rebel forces" have taken out other telepath controlled cities, thus proving they are not invincible and probably stoking the fire of resentment of the current population, or they keep their mouths shut and silently mind read in horror as the population gets word of how the telepaths were defeated in other cities and now the normal people get in their heads that mind readers can and should be overthrown.
That is more on the ideal end of the spectrum. A darker end could be with the plan not really getting anywhere and being doomed from the start, similar to 1984. The resistance could be defeated before any rebellion begins due to internal problems. The rebellion itself could fail to either sway the population or even take out the telepaths to even get a stepping stone. Even with one city liberated, the country could unite against he "rebel aggressors" instead of joining them. But those would be story specific details - for a world detail, I suggest a resistance force working beyond the range of the telepaths who try to slowly manoeuvre everything into place and then do a blitz-rebellion to overthrow the telepaths.