I managed to hacked myself to build a habit of 30 minutes a day of spaced repetition, building off my momentum to consistently do khanacademy an hour a day(A project which I finished a while ago) in conjunction with my time tracking tool. The key seems to be a bunch of small repeatable goal that allow for small wins. It works for me, though I don't know if it will work for anyone else. Plus, it's only anecdotal, so take it with a grain of salt.
(I wish there is a accessible book that rigorously about which habit building strategies work according to scientific research)
If you're talking about Tiny Habits, I can vouch for it since I took it end of March this year. Of course my word's not worth much but BJ Fogg does explain about the method on his blog:
http://www.foggmethod.com/#large-media and http://www.behaviormodel.org/
so in that sense it isn't like the "fitness/attract opposite sex" programs (scams) you talk about where everything is hidden and shrouded in mystery.
It's all automated via email, so it can be free. It is quite simple and effective but applying the rules in a general sense is something you'll have to master over time.
Also although BJ Fogg has my email address, he's never tried to sell me anything after the program finished, even though I note from his updated site he's got a new certification to be a coach program going on.
(I wish there is a accessible book that rigorously about which habit building strategies work according to scientific research)