During your nail care routine, be very careful about filing down the sides of your nails. If you're not extremely careful, you're just asking for a split, since this kind of filing weakens the nail. Don't let your professional manicurist do this either.
Nail-biting is one of the worst things you can do, in terms of nail care. Not only does it result in ragged and unsightly nails, it can weaken the nail and causes splitting and unexpected breakage. Plus fingernails, if swallowed, can play havoc on the digestive system.