Buy yourself a ring. Buy two. Buy ten.
I bit my nails to the quick and made them sore and bloody for twenty-one years. Then, I got engaged. I could not stand the sight of my gorgeous engagement ring on my nasty fingers, so I quit biting my nails.
Treat yourself, if no one else offers. Buy expensive, beautiful rings that you love! Wear them often, and every time you go to bite a nail, look down at your rings and remember how ugly they will look with ragged nails. Soon, you will want to start filing your nails and applying strengthener in order to further improve your hands' appearance. After some time, if you keep your willpower, you can break your own habit!
Obviously, this is going to be harder if you're a man. I'm not sure what to suggest for that. If you're short on money, only buy one or two rings, and remind yourself that you spent hard-earned money on them and that you owe it to yourself financially-wise to keep your hands looking nice in order to justify the purchase of the rings. I'm sure this won't work for everyone, but coming from someone who tried everything, it's worth a shot!!!!
Good luck!