I bit my nails for 20+ years. TWENTY. It scares me that I'm even old enough to say that, but I have done it ever since I was a kid. I have tried so many times to stop, pretty much every New Year, with limited success. The last time was going great until the League One playoff final in May 2013... so in June 2013 I decided I was going to start again, and for the last time.
If you bite your nails you'll know how hard it is to stop, and not only that, but how weak and brittle they are if you manage to grow them. Get a tiny chip, and that's dangerously tempting to bite, or constantly pick at.
Thankfully help is at hand with the miracle that is Sally Hansen hard as nails treatment. This stuff makes your nails grow faster and stronger, thickening your natural nails to ensure minimal breakage and chipping. Without this stuff, my nails are still much improved, but if I'm wearing this my nails are virtually indestructible!! On the left, without, on the right, three coats on top and underneath.
I wear at least three layers of this under any polish. It's really quick drying so no biggie. It's not very shiny so if you want to put a clear top coat on, I recommend Sally Hansen Super Shiny, which also helps to strengthen. I also put this on the underside of the nail, the second they were long enough. You may need a thinner brush for this rather than the standard one at the start. And yes, it will probably go on your skin too. A small price to pay for the awesomeness!!
This stuff also tastes rancid. I mean proper nasty. Another way to put you off biting them!!
Once you have put a good few layers of this on, get a brightly coloured polish that you love and put on a couple of coats. It may look stupid on really short nails but trust me, it will really make you think twice if you see bright orange when you go to put your fingers in your mouth!!
Always always wear polish, even if it's just the Hard as Nails stuff and a topcoat. The prettier they are the less likely you are to want to bite them.
Always have a nail file handy - I have one in my handbag, one in the car and one on the coffee table. If you get the tiniest chip, rectify it as soon as possible. This reduces the temptation to pick at it or to bite it just to "even it up" (used that excuse many a time...)
Unfortunately the last thing you need is willpower. But stick at it. Once you get enough growth that they look pretty and you can buy nice polish and do nail art, it will be massively worth it!!