Nothing.
Are they red? I only ask to make sure you don’t have some sort of fungal infection. Then you might want to try something for athletes foot.
If not red, then let’s just assume dry. If you don’t use lotion, just try any lotion daily and see if it helps. If you already use lotion, then try petroleum jelly one night, remember it can get grease on your sheets or carpets, which is very hard to remove, so be careful. Use it even just for a few hours in the morning on a lazy day, and then take a shower to remove the excess.
Vaseline heals dry skin and lips like no other in my experience. In one day the difference can be dramatic.