I remember when I was a kid that my mom, teachers, and the adults on "Arthur" were always telling me to not bite my nails. I don't know why that appeals to little kids or why it's sometimes so satisfying, but for some little children it's irresistible. Alas, for many of us that habit carries on with us into adolescence and even into adulthood. The fact is that nail biting is an unattractive habit and one that greatly affects the impression you have on other people. Keep the few following tips in mind as you free yourself from biting your nails.
First you need to realize that biting your nails is actually a big turnoff to anyone, whether it be in a friendly, romantic, or professional setting. It puts your appearance into a childlike mold and many can find it hard to take you seriously after seeing you indulge in such a juvenile tendency. Second, think about what you're doing to your nails. You're not making them more attractive by any means, but rather you're making them ratty and scraggly and quick to snag on clothes, cushions, and just about anything. Biting your nails is also bad for your teeth. If you've noticed, when you bite your nails and some of you may try to "file" your rough nail afterward with your teeth, but your teeth are strained a bit and it's most definitely not such a stellar idea.
I think one way to break the habit is by getting a manicure (or even just giving yourself one) so that your nails feel pretty. If your nails are pretty to begin with, you'll be much more apt to think twice before putting that nail between your teeth. (Plus the nail polish could very well leave a nasty taste in your mouth—ew). Focus on maintaining healthy and pretty nails and you'll not want to subject your nails to such a rough treatment.
One tactic I've found that's helpful when my nail snags or get a rough edge, is instead of resorting to biting off the affected part of the nail (which usually leads to more rough edges and consequently more biting) is to carry a nail file with me. When I have my own emery board, I have much better results when smoothing out uneven edges and don't have to deal with an even rougher nail or the nasty bits of torn nail on my jeans.
Breaking the nail biting habit may take a few weeks, but it will most definitely be worth it. Who wants to come off as childish or have an even rougher nail than before? This may take a degree of self discipline, but it will without a doubt benefit you greatly in the end.