I bit my nails all through my childhood. When I became a young adult & wanted to stop, I started carrying a nail clipper in my pants pocket. As soon as I felt anything like a ragged nail, etc., I trimmed & / or filed it down so as not to be constantly reminded it was there. Also, I kept my nails trimmed short to begin with. This, plus my desire not to bite my nails any longer, was sufficient to break me of the habit.