I'm not claiming this works for everyone but what sometimes work for me to form a routine is to do the thing but without committing effort to it. I.e. go to the gym but you only promise yourself to go there, not actually spend effort there. Any actual exercise you then do is a bonus, not a "payment on your promise".

I think it can be generalized as:

Find the thing to do that doesn't require much effort but puts you in the context of doing the effortful thing. Do that thing. See if you "want" to do the effortful thing. Otherwise go home.

Cleaning? Put the vacuum in your hands and see if something happens.

At least I think that's how it works for me.

The points when it's hardest to make it work is when there's lots of distractions. Like when you try to get into a routine of doing work at a computer.