-Have a practice program with various aspects (drills, different kinds of games etc), write down your thoughts at the end of the day, just a few lines, read them over and reflect on them every week.
-Meditation is good, in terms of preparing yourself for dealing with stress during matches, imagine being focused, breathing well, playing the table vs the opponent etc. It's a bit like "camera visuals" before executing a shot regarding shape, it usually helps if you see the CB going to the desired area before taking the shot.
-A little nice focus exercise I learned from World champion Oliver Ortmann, let your eyes focus on the light of a candle placed aprox. 2 meters away from you, for 30 seconds, stop, repeat and so on. Good for approaching target spots better when playing.
Best,
Petros