how do you stop a bad habbit?

If it's a problem like smoking, try going for longer and longer amounts of time without doing it. Same for biting fingernails, etc. Another thing is to think about what you don't like about the habit--if you eat too much, for example, think about how you'd feel and look better if you lost some weight. You can use this technique for any kind of habit--think of the positive aspects of breaking the habit, and that will encourage you to change your behavior.

The fast rule to break the bad habbit for me is just to realize it that is bad and say to myself STOP. Sometimes it works. When it doesn't work, then I guess time will also help me in breaking the bad habbit. As long as I am willing and have some guts to break it, then there shouldn't be a problem.