[BillGoatse]

I quit that years ago (almost).

Start by not biting one nail (left pinkie is good). Get that down (take pride in it. make it your friend :) ), then 'save' the left ring finger too. Carry on up the hand, but jump to stopping the whole left hand as soon as you're confident (become a right hand biter!).

Then move on to the right hand pinkie etc.

I made it as far as my right thumb, which I still chew when I'm thinking.