I have been using the rubber band negative reinforcement technique to help stop me from biting my cuticles and it has been working fairly well. Whenever I find myself putting my fingers in my mouth I "punish" myself by snapping the band on my wrist. I have gotten to the point that I now recognize that I am about to starting biting and stop myself. I hope that I will eventually stop even before I put my hand near my mouth.
Habits are really hard to break. One has to change their entire way of thinking and deviate from a comfortable, normal-feeling activity, to another one that is outside our comfort zone. It takes time, effort, and thought. I have heard that it takes the average human about 2 weeks to develop a new habit and 90 days to break one, so I am giving myself a little time. I know that when I started riding my bicycle for exercise, after a few weeks, it was engrained in my daily routine and I didn't even think twice about it and it felt odd when I wasn't able to do it.