Research shows that people who successfully change their behavior don't do it all at once--they tend to go through a series of stages. Psychologist James O. Prochaska, author most recently of Changing to Thrive, has identified six stages and the strategies or tools you should use at each. He outlines all this in his Transtheoretical Model of Change, which is based on extensive research into behavior change.
According to Prochaska, it is important to recognize where you are in the cycle of change--what your "readiness for change" is--so you can set appropriate goals and action steps and determine the best strategies. To elaborate, if you set goals that you are not ready for, you set yourself up for failure. Similarly, if you choose goals that you have already mastered, you will delay your progress. But if you match your goals to your stage of change, you will maximize your ability to change.
The descriptions of each stage listed are taken from Prochaska's book Changing for Good.