Biting your cheek out of habit, is as stated, a habit, like biting your nails. Just work hard at not doing it. If your biting your cheek because your teeth are not aligned straight, you could see an orthodontist. People that "chew" on their cheek out of nervousness or anger, create a white callous mark in their cheek. And any white area in the mouth is referred to as a leukoplakia (dental terms). If you are constantly chewing off the top layers of your oral tissues, yes, it could one day become a cancerous lesion. So stop chewing!!
If you bite your cheek on accident, you can get some Zilactin B for oral lesions. You can get this over the counter at any place that sells oral hygiene prouducts(toothbrushes, floss, paste, etc.) Look near the ambosol in comes in a red tube and a blue tube. Out of experience, I think the red tube sticks better. Follow the directions exactly, and be sure that the area it is applied to is plenty dry. At home I like to use a blow dryer to dry, and a cue-tip to apply it, then dry it again. Basically it forms an oral band-aid, and keeps it a little numb to the pain. But it ususally stings when you put it on. It is also good for canker sores that are inside the mouth.