Your question is a bit vague on why exactly gods need belief:
They somehow screwed up when creating the world and now require worshippers to not die?
It turns out mortal can generate copious amounts of a Very Important Resource and they want it for pantheon domination, further world-making and/or for use as poker chips?
They prefer to have their worlds infested with obedient little sapient annoyances to having their worlds crawling with unruly little sapient annoyances, because the former are more likely to scurry away when you need them to scurry away?
and, more importantly, what kind of belief they need: fanatical devotion, love-filled faith, fearful reverence, any-kind-is-fine?
In quite a lot of cases, killing the mortals who dare to waste your time with their incessant nagging is a perfectly fine solution as long as you do that immediately after they ask you in public, preferably surrounded by common folk and believable witnesses, so cause-and-effect relation is crystal clear and the word spreads. This way, you can get quite a lot of hushed, terrified belief and establish yourselves as the "Stop, you violated the
law natural order!", "there's a long list of things they really don't want you to do", "like Olympians but without favours" kind of gods.
Of course, you would probably need to do some other tricks from time to time, but eventually your position should be cemented and people should stop asking.
However if that kind of public image is not a viable option,
you might want to rethink why your gods are doing everything to set it up there are two other options.
The most effective route has already been mentioned by others: you need to tell them. Either directly (word of god, pieces of writing ascending down in a beam of light) or indirectly (pass down the holy commandment that taking even more from the gods than they already gave you is unclean, abhorrent and sinful).
The second most effective route would be to take inspiration from stories about monkey paws, deals with the devil and lazy/malevolent genies, and grant every single wish - but grant it completely wrong, tongue-in-cheek, bonus points if it results in some sort of a visual or a situational pun.
I can't think of a good example, but, let's say:
A general asks for an army to defend him from incoming horde? Spawn 50 chickens in adorable, tiny, completely useless helmets. With manicured, completely dull claws. And make them inedible, too (you can't eat something that poofs out of existance when it's poked too hard). And when he repeats himself, spawn another 50 slightly above his head, because slapstick. And if he tries to explain he needs something ferocious, make the chickens peck away his good boots, his fancy prayer pants and his oh-gods-I-paid-four-villages-for-this cloak.
(And have them immediately pass out from exhaustion, of course. We don't want them to be too competent.)