Summarize:

Deep breathing, also called diaphragmatic breathing, helps you relax both physically and mentally. Research has shown that using this technique during times of stress helps alleviate symptoms of stress like lip biting and other bad habits. When you feel the urge to bite your lips, try doing this instead:  Sit up straight so that your torso is perpendicular to the ground. Take slow, controlled breaths that fill your abdomen. You should feel your stomach moving in and out. If your chest is moving up and down, you're breathing is too shallow. Focus on breathing deeper. Continue deep breathing until you feel relaxed and no longer want to bite your lips. Deep breathing is commonly included as a step in habit reversal techniques. This is another physical technique with profound mental effects. It takes several minutes to complete. Do this technique in times of great stress to resettle yourself and stop the urge to bite your lips. Like deep breathing, this is also a common step in habit reversal techniques.  Tense the muscles in your arms as hard as you can. Breathe in deeply and hold your muscles tight for five seconds. Exhale and release the tension at the same time. Stay completely relaxed for 15 seconds. Choose another muscle group to tense for five seconds. Try your legs, torso, buttocks or jaw. Continue alternating between tensing and relaxing until you've gotten to all the main muscle groups. Keep going until the urge to bite your lips passes. You may need to rotate between muscle groups for up to fifteen minutes. Mindfulness is the act of being fully in the present. When you pay more attention to your body and how it feels, you'll be less likely to bite your lips absent-mindedly. Mindfulness takes a bit of practice, but once you get the hang of it you can use this technique anytime, anywhere to great effect.  When you feel anxious, immediately focus on your five senses. What do you see in front of you? What do you taste in your mouth? What do you hear around you? What do you feel with your hands? What do you smell in the air? Keep focusing on your physical state until you ride out the anxious thoughts. If you're having trouble focusing, try the quick trick of looking at your hands while you clasp them together. This will help to ground you in your body immediately.
Practice deep breathing. Practice progressive muscle relaxation. Practice mindfulness.