Always try to maintain a ritual before your matches. They could be complex or very simple. Just like going to bed and waking up at the same time every day is important to your health and bio-rhythm. A ritual can do the same thing for your tennis.
For example, practice a 10 to 15 minute warm-up as a ritual for success. You might start off tapping the ball off the bounce, back and forth, with the ball landing inside the service line. Then hit baseline to baseline, then hitting one up at the net and one back on the baseline, practicing exchanging volleys and overheads. After that, you could hit a few serves and returns, finishing with some points played out on the cross-court for doubles and full court for singles. Each of these scenarios would only last 2-3 minutes. Do this until you can get everything done in a short time period, 10-30 minutes total.
When you are practicing, do the same drills in the same order, just extend the time frame. This could be a 1 hour to an hour and a half workout on practice days.
The confidence and calmness that you will gain by doing this ritual will be tremendous. This way, if your opponents do not give you a good warm-up, it will not matter. You will be mentally and physically ready to start the match.
Good luck on the courts!