The main thing is to keep the vent itself open. The danger is when the dried poop prevents their pooping, which can actually be lethal. And the main thing for that is to keep them hydrated and not too hot. Very young chicks often foul their water quickly, so it may need some attention. Put it up on a brick or similar if you can. It's important for them to be able to move away from their heat source to wherever they are comfortable. If you have some, a little organic ACV (apple cider vinegar) in the water does seem to help. Some also use a little molasses.
Also, if you do have to clean a few butts, put a little lubricant around their vent to discourage future poops from sticking. You can use Vaseline, veggie oil, Crisco, even Neosporin -- whatever you have. I found it easiest to clean them by holding their back end under a slow stream of running warm water. It takes a few minutes. If I didn't get every fleck off every feather tip, frankly, I didn't worry about it. It shouldn't be a problem as long as the skin doesn't have any open cuts or abrasions.