When I was a kid I used to bite my nails. My brother and my dad used to nag me all the time to give this habit up, and I did a couple of times, once after being bribed with a pet hamster... I don't know when I started but I think I was about 13 or 14 when i quit for real and what helped me was to paint my nails. A lot. In a hundred different colors and all kinds of patterns. Nowadays I don't paint them as much or as creatively - though I still have 50 bottles of nail-polish or so, many of them actually dating back to my teenage years. I used to collect colors.
My nails have been in an horrible condition for the last few months, maybe it's because I don't drink enough water, maybe I don't eat enough B-vitamins, but they just keep peeling all the time. I try to get them back in shape by cutting them short and yes, painting them, so I kind of have rediscovered the fun of fancy nails. This time I tried bright red with a pink fake lunula. Did you know that's the name for that half-moon shaped, white inner part of your nail? Now you do.