Mindfulness: Whenever you catch yourself performing the undiesrable habit, watch your thought patterns. If you think "Ugh, there I go again, failing to remove my bad habit", you'll have a rougher time than if you think "It's okay, I forgive myself for this slight lapse."

Beyond that mindfulness, if it's hands specifically, I do pen tricks, tap along to my music, plant my hands on my sides/thighs, and generally keep my hands away from the problematic habit.