To play table tennis effectively, you need to have a calm, clear mind, which allows your training to pay off effectively. How often have you actually played a tournament where you entered every match with a calm, clear mind?
Shortly before your match starts, simply go off somewhere where it's quiet. Close your eyes. Blank out your mind. Relax. Do this for perhaps 10-30 seconds and you're ready to play. (There are more advanced techniques for doing this - Google "sports psychology table tennis" - but for many of us, this is sufficient. Some do it longer or listen to music.) Corollary: when you're at the table and the warm-up is over, and the match is about to begin, take 5-10 seconds to do the above again, and perhaps every now and then during a towel break or other timeout.
This doesn't mean you should be lethargic. Some players (including me) need to get "psyched up" to play well. But you can do that while keeping a calm mind. Before the match, perhaps do some exercise to get the feet going, perhaps jumping up and down lightly or shuffling side to side - but only a for a short time as you don't want to go into the match tired. During the match, do the same sometimes between points, as you'll often see world-class players do. (Older or out-of-shape players might do this less to save energy.) Keep encouraging yourself each point to move and take your shots. If you celebrate after winning a point, that often helps relieve tension, but make sure to clear your mind before starting the next point. A cluttered mind leads to klutzy play. A clear mind allows your training to take over.