The tips I use, that I also use with the players I coach are:
-Develop goals for each match that are outside of "winning"
-Get a good team around you that is able to encourage you (and not just help you how to hit a good forehand) - anyone can show you how to play technically well, but if the teams not in your head supporting you, you aren't going out there and hitting that great forehand shot you practiced in training
-Play like you are ahead.
-Practice breathing exercises on court.
-Realise that winning a tennis match isn't life or death. there's life outside of tennis, so enjoy the opportunity you have to compete at the highest level.
-there's plenty more but that's a start