How we form habits, change existing ones -- ScienceDaily: "... According to Wood, there are three main principles to consider when effectively changing habitual behavior. First, you must derail existing habits and create a window of opportunity to act on new intentions. Someone who moves to a new city or changes jobs has the perfect scenario to disrupt old cues and create new habits. When the cues for existing habits are removed, it's easier to form a new behavior. If you can't alter your entire environment by switching cities-- make small changes. For instance, if weight-loss or healthy eating is your goal, try moving unhealthy foods to a top shelf out of reach, or to the back of the freezer instead of in front.
The second principle is remembering that repetition is key. Studies have shown it can take anywhere from 15 days to 254 days to truly form a new habit. "There's no easy formula for how long it takes," Wood says. Lastly, there must be stable context cues available in order to trigger a new pattern. "It's easier to maintain the behavior if it's repeated in a specific context," Wood emphasizes. Flossing after you brush your teeth allows the act of brushing to be the cue to remember to floss. Reversing the two behaviors is not as successful at creating a new flossing habit. Having an initial cue is a crucial component." (read more at link above)