Cheek and lip biting. Cheek and lip biting is a nervous habit and takes a conscious effort to stop it and time.
Will power. This is a common habit that people have similar to nail biting. I myself have been a nail biter and its a very hard habit to get rid of. The simple answer is will power. You just have to notice when you are biting your cheek, what causes you to do it? Stress? I just talked myself out of the habit because i knew it was nasty and made my nails look bad. You might also try counseling or hypnosis.
Hard to do. Like any habit, such as chewing fingernails, it can be hard to do. But is a great goal to have because chronic cheek biting is not good, and can lead to cellular changes that are bad. Everytime you catch yourself doing it...Stop! try chewing sugarless gum instead. Eventually you will kick the habit. Good luck!
Hard to stop but.. You may need a bite appliance to wear at night and even during the day to break the habit.