this is going to depend upon the cause. Ulcers? Salt water is good for some infections but you might need something more specialist.

if it's just the lips which are chapped then you need to treat those differently, eg with vaseline if you don't go in for expensive lip balm.

visit a dentist?

usually an over-the-counter mouthwash helps.

Depends on why. The two things I've used is a saline rinse, and using clove/clove oil. Oh, sef mentioned like lip related stuff... So... Yeah there's that.