I'm not semi-pro but I would expect spending hours with GTO solvers and other poker training software will play a large part in it. The idea is to get quick feedback on how well you are judging difficult situations.
Some people also have to spend a lot of time working on emotional regulation to avoid throwing good money after bad.
> emotional regulation to avoid throwing good money after bad
I was once interested in going pro, and I landed on some advice that said to go to a poker house and fold every hand for 3 hours. Poker has very high variance, and you can easily have 3 hours of hand shuffled poker and not get a single playable hand. That was when I realized I didn’t have the emotional regulation to play properly, especially, since part of the exercise was to throw away the strongest starting hand even if you are dealt it during this exercise. Also, that was about the time I realized that poker is generally an extremely boring game, with the very occassional periods of high emotion.
It did teach me a lot about going on tilt though, it’s very easy to throw away a lot of profit after a big loss.
Some people also have to spend a lot of time working on emotional regulation to avoid throwing good money after bad.