I was successful in keeping a strict (but light) exercise routine for a year. Here are the main things I think helped me form the habit:

• Not worrying about quantifying, or optimizing. I would immediately get into the rabbit hole of analysis, when I knew that any exercise was much better than procrastinating until I found the perfect method. Once the habit is formed, then you can optimize it.
• Reduce physical inconveniences to actually exercising. The thought of going to a gym immediately turns me off, so I knew it had to be a home. That meant obtaining equipment. To keep it simple, this consisted of a yoga mat and a resistance band.
• Doing it right after waking up. I think this was vital to habit formation, as my mind isn't very active, and it was easy to fall into routine. Only very rarely did I find myself considering not exercising.
• Doing it every other day - not too often to get burnt out, and not too infrequently to form the habit. In order to keep a consistent sleep schedule and not have to wake up very early, I alternated morning routines - exercise days and shower days. My workouts weren't intense enough to necessitate a shower immediately after. Also, I worked it in with my intermittent fasting routine on non-exercise days.
• Tracking it. Noting days that I exercised did give me a couple of achievement hedons. The effect diminished, but not before the habit was formed.

All that said:

• It only took a week-long vacation that disrupted my routine to convince myself that it was a good idea to stop the routine in order to see how it affected me. ...That was about 4 months ago.
• I don't think my specific workout had much of an effect on me physiologically. The note above about optimizing after the habit was formed - well, I never took the effort to begin quantifying and tracking detailed progress or optimize the actual workout.
• However, I do feel like I've become more stress-able, physically and mentally, so I do plan to restart a routine after holiday vacation.