Think about why / when you do it. Write it down. Write down why you would like to stop. Write down what benefits would come with stopping.

When you’re about to start biting, or catch yourself biting, take a big deep breath. Put your hands away. Keep breathing. You’ll see you CAN stop. And after doing this for just a short time (I’d give it about 3-4 days), your skin and fingernails will look so much healthier, hurt less, you’ll realize how germy it is when you do put them back in your mouth, you’ll feel proud working toward your goal etc etc.

First couple days will be the hardest and then it’s smooth sailing. If you find yourself doing it again, be nice to yourself and try again :)