As someone who got into a regular exercise habit a year ago that has progressively gotten more intense, I disagree with a few of your points.
Actually, I guess it's mostly the first 3:
> 1. Build a routine. Set a specific, repeating time when you will do the thing in your calendar. Keep that slot clear, ALWAYS. Never let something interrupt this task.
> 2. Learn to say no. If someone wants you to do something else during this time slot, say no, and tell them why.
> 3. Never break the routine. Breaking it once makes it MUCH easier to break the next scheduled time. If you do break it, feel bad about it and get back on the horse IMMEDIATELY.
It's this "do it now or feel guilty" stuff that keeps most people procrastinating or avoiding doing the task. I remember initially I would have it set in my mind that I needed to go to the gym at 10 a.m. the next day. If I woke up a bit late or was wasting time on reddit and 10 a.m. looked unrealistic, I started feeling really guilty. "Oh no, if I don't go now, I'll never go!" It put a lot of stupid, unnecessary pressure on the situation. And it didn't really have the desired effect -- I'd usually not go, since I had already blown it by missing my 10 a.m. deadline, after all!
Now, I might wake up and plan on going at 10, but I know that I 1) absolutely do plan on going and 2) can go at 11, or 12, or 1, or 2, etc. There's no need to make the task worse by associating a lot of negative pressure and guilt with it.
> One thing at a time. [...] Leave time in your schedule for play.
Totally. Especially if it's an area where the amount of information out there can be overwhelming (a la fitness / weightlifting). I started out going with a few exercises I enjoyed in mind and simply did them until I felt tired. I didn't worry about making a program, writing down my workouts, obsessing about nutrition, or obsessing about how many days or which days I did what.
Over time, things started getting easier and I began incorporating more of this stuff as I started feeling comfortable. But the initial phase where I made the habit something I actually enjoyed was crucial. Even now, when I occasionally find myself feeling like I've slipped too much back into treating it like a job, I take a day to not keep track of anything and try some new exercises that I think might feel good.
Edit: Also super useful:
> If you can find someone who will hold you accountable, do it. Someone who does the routine with you, or a coach who will call you out if you make excuses.
For me it was my roommate. I'd go with him the first couple of months. After a while I felt comfortable enough to go by myself and do my own thing, but that initial time where I would use the slight social pressure of him going and asking me if I wanted to go to keep myself in check.