To break a bad habit, engage in a replacement behavior immediately after the bad habit is executed.

“So it turns out that the key to generating long term depression in these pathways is actually to take the period immediately following the bad habit execution, meaning, let's say you tell yourself you're not going to pick up your phone, you're not going to bite your nails, you're not going to reflexively walk to the refrigerator at a particular time or day, but you find yourself doing it anyway, and what actually has to happen is bringing conscious awareness to the period immediately afterwards, which I think most people recognize, they realize "Ugh I just did it again.”