From the field of addiction counseling, James Prochaska researched and developed a theory of readiness for change in people that is pretty well defined. The six stages are also a useful exercise to consider when thinking about behavior design in your product.
Stage 1: Pre-Contemplation
During this stage people are unaware for their need to change. Using assessment data that is specific to that user can help raise the awareness for change.
Stage 2: Contemplation
People are considering making a change when in this stage, but are often unsure how to proceed. They often struggle with whether making a change or taking action is worth it and will get stuck weighing the pros and cons of making a change.
Stage 3: Preparation
A person moves to gathering information, and lining up resources, or gathering options in order to make a change. This stage is a pivotal transition from thinking (Stage 2) to doing (stage 4). This is where a product or service can play a pivotal role in facilitating behavior change in individuals.
Stage 4: Action
This stage is where a person is actually trying new things and taking action.
Stage 5: Maintenance
Persisting with an action long enough for it to become a habit or routine is the hallmark of this stage. making minor modifications or tuneups to a persons plan based on their environment is key.
Stage 6: Termination
This term is used to simply signify that the person no longer needs any kind of programatic system to help facilitate change because key actions have successfully become a natural part of their lifestyle.
These six stages are not always linear and a person could be in multiple stages at the same time while addressing multiple behaviors.
Williams, Patrick, and Diane Susan. Menendez. Becoming a Professional Life Coach: Lessons from the Institute for Life Coach Training. 2nd ed. New York: W.W. Norton, 2007. 76-79. Print.