It is not always in your advantage to serve first unless you can serve at 120 miles per hour. In general, holding your serve is not as critical at the club level as it is in the pro ranks. Thus, by allowing your opponents to serve first, you might get an early break. And, if you don't, you/your team will already have played 1 game which will allow you to settle down and be more focused for your serving game.
Early in the warmup, try to figure out which opponent is stronger and which is weaker. Make note of any apparent strengths and weaknesses and never allow your opponent to beat you with his/her strength.
The most important time in a match is the last 10 minutes you have before you play. During this time, you should picture yourself playing. See yourself being successful in many different scenarios.
Use the elements to your advantage. For example, lob more into the wind and force your opponent to look into the sun to hit overheads.
Also, when you hit a poor shot, don't assume you are going to lose the point. Stay in a defensive position and make your opponent hit a great shot to win the point. Play the point until its completion - don't run off the court!