Regular manicures. Start with a light-colored polish, like OPI Bubble Bath.
I LOVE that color! It's the only color I'll paint my nails. It's so sheer and feminine. It helps me not bite my nails when I look down and see how pretty they are when painted with Bubble Bath
What stopped me was realizing that we use our hands for everything, and unless you scrub your nails like a surgeon every.single.time you wash your hands, God only knows what nastiness you are putting in your mouth...
I am an avid nail biter. I have slowed down on the actual biting part but I still chew, bite, and pick. I try my hardest to keep them painted and I have managed to grow them to a considerable length. They actually look pretty.
As far as thinking about whats under my nails, I dont. I just mindlessly chew them or bite them especially when I am stressed. I'm trying to quit all together biting, but I dont think that will ever happen.
I've bitten my nails for as far back as I can remember. I tried many times to stop but it never really worked for more than a month or two. What finally broke me of the habit was I got invisalign to straighten my teeth. I couldn't bite my nails through the snap on trays...and a lot of times my teeth felt too sore and weak to try and do it anyways.