If you've ever felt powerless to avoid biting your nails or indulging another bad habit, it's because to some extent you are. Our brains are programmed to promote habits - whether they be good or bad.
Our brains like habits because routines require little thought, which gives our minds a chance to conserve energy while our bodies run on auto-pilot. So the best way to break the bad ones is to work with the way your brain and replace one behavior with another.
For nail biters, it's helpful to understand when and why you compulsively gnaw your cuticles. Many bite because of boredom, so noting when boredom tends to set in during an average day is crucial to reprogramming your brain. Then, when you begin to feel bored, you can try to break the habit with a healthier form of physical stimulation, which can be as simple as stretching or tapping your knuckles on your desk.
Sometimes we develop bad habits that are attached to positive routines. People who buy cookies or other fattening treats have found that their hunger for snacks is actually a craving for human interaction. So instead of chatting with the person behind the counter, they skip the snack and chitchat with a friend or co-worker for a few minutes to indulge that social stimulation.
For more tips, check out this video from AsapSCIENCE.