[katzgrau]

First, set a cue. If you're going to the gym, perhaps it's always right after you wake up. You need to have a cue that consistently happens. After a while (a month), it becomes habit. Simple waking up sets off a whole sequence of habits for me.

Next, for the things you want to improve on, set a goal, measure and track.

For each exercise, how much weight did you lift, how many reps? Write it all down and match or beat yourself last time.

Start small so it's not overwhelming, and improve incrementally from there.

That's it. And even if you don't feel like doing it one day, take the first small step to doing it - like getting dressed for the gym. Then see what happens.