A regimen is a systematic plan that is designed towards preservation, improvement, and maintenance of health. This plan most times come in form of medication, diet, any type of therapy, exercise, and lifestyle. The main aim of a regimen is to achieve a positive result. The result you seek depends on what area a regimen is designed.
For instance, an athlete who desires a better performance could follow an exercise regimen particularly designed to achieve that. A hospital patient with a certain medical condition could be placed on a particular diet regimen in order to improve their health. Again, an individual who desires to maintain or preserve their health could follow certain lifestyle regimens such as quitting alcohol consumption, smoking, and any other lifestyle which they perceive to negatively affect their health.
All in all, your regimen could be anything, however, what matters is the healthy and positive result that comes with it.