Pick a particular new behavior that you want to turn into a habit. Express it in writing in the form of a positive goal. Such as"I will exercise at least 45 minutes a day"
Repeat your written goal to yourself as often as you possibly can while visualizing yourself doing the exact behavior that you have written out and are affirming to yourself. Be positive, be excited.
Commit yourself to your new behavior by performing it whennever it is appropriate to do so.
Let others know that you are committed to a new behavior and encourage them to tell you when you have fallen back into your old behavior.