Nail-biting is a tough one. Without a reasonable doubt, it is a very satisfying habit. The best advice I can offer is to get rid of the nail polish, and use iso-propyl alcohol instead, it is absolutely foul. It is very strong and helped me to stop biting my nails. Becoming aware of the habit when under social circumstances can be difficult, because our conscious thoughts are being directed towards absorbing the situation going on right in front of you. A good exercise would be to take 10-20 minutes of quiet alone time per day, to re enforce your goals. Simply tell yourself you're going to stop, yell it in the mirror, meditate on it, write it down 50 times. Do something so that it becomes apart of your natural thought process. This may seem like a lot of work just to stop something as simple as biting your nails, which is why most people with the habit carry it to their graves. You need strong resolve to stop subconscious habits, to the point where it may not even be worth your time. However, if you feel strongly enough about the aesthetic and/or health benefits, then take my advice. It will work.