Try to force it as little as possible and use lip balm or moisturizer that will help it stretch out less. You should also avoid smiling and laughing too much for one or two days to allow the surface skin to get back in it's original shape and heal completely.
Drink lots of water and eat foods rich in vitamin A. Gently scrub lips and rub olive oil or cocoa butter on lips. You can also chop cucumber and rub on the lips. Petroleum jelly may also work.
I actually prefer Vaseline with no additives (some vaseline products include paba, which I'm allergic to). You should also make sure you're well hydrated, since dry skin results from dehydration.
Try non-waxy lip balms, such as Blistex. If that doesn't work, apply Vitamin E in liquid form at night: it is tasteless and comes in small bottles. Stay well hydrated.
