Overlearning, shaping and chaining approaches use conditioning principles to establish new patterns of behavior; new learning. However, sometimes your problem is not that you need to learn something new, so much as that you need to unlearn something old. This is often the case when you hope to alter established and ingrained habits. By definition, habits are something you do habitually, without thinking. They occur automatically and for the most part, unconsciously. Habitual behaviors usually occur in chains (as in chaining, above). This means that some initial stimulus sets them off, and then a sequence of events occurs that ultimately results in the occurrence of the behavior that you want to avoid. Habit chains are set off by "triggers" (stimulus events that bring them into mind and which reinforce their execution). Once a trigger sets a habit chain in motion, it is difficult to stop it: You either don't notice that it is happening, or it plays with your mind so that you don't care.
You can interrupt and (over time) alter your habits by applying learning theory-derived techniques to them so as to gain back conscious control over their execution. Self-monitoring exercises help you to become aware of your triggers and the other rewards and punishers in your environment that control your habit. Once aware of these influences, you have the opportunity to alter them, or your susceptibility to them. If you succeed in avoiding your habit for long enough, it will naturally weaken in strength, due to a process called extinction, and you will ultimately become free of it. This is much easier said than done, of course.