Try to "change" things up on the serve. If you can get free points on your serve, this will allow you to win your service game with a lot more ease; allowing you to move on and focus on breaking your opponent's serve. How to mix things up: firstly, by serving at different speeds. Secondly, by aiming at different targets in the service box, and lastly, by using different serves (flat, slice, spin serves). Remember, you always want to keep your opponent guessing!

see Mark Tiu's profile

When playing  the net behind your partner’s serve, be active. If your server serves out wide, shift and cover the alley.  If your server serves down the middle, shift to the middle and cut off any balls through the middle. On all serves, first and second, stay on your toes trying to anticipate the return. Communicate with your partner, poach occasionally, try different formations, and throw in a fake once in awhile, but “DON’T BE A SPECTATOR AT THE NET!”

see Tim Butorac's profile

A key to your singles and doubles game is your ability to react and anticipate. Try and pick up on your opponent's tendencies and you will be able to cheat with your positioning. Always be balanced and ready to move in any direction as your opponent is hitting to make up for a lack of foot speed. I've noticed this to be more important the older and slower I get!

see Kyle Anderson's profile

There are three common mistakes that I see many players make when playing doubles. One is standing too close to the alley when your partner is serving. The net player must be in a position where they can cover any ball that travels through the middle of the court. It is not the server's job to cover three quarters of the court(except Eric in Father/Son doubles)

   The second mistake is trying to go down the line too early. Try to keep the ball cross court until you have a high volley where you can end the point at the net player. If you go down the line too soon, a good net player will make you pay the price by reflexing it back at you.

   The other common mistake I see is a server trying to annihilate every single first serve and then tapping in the second serve. A smart approach is to hit a three quarters pace first serve with more spin. This will give you a higher percentage of first serves and also allows you extra time to come in behind your serve. You don't want to be coming in off a weak second serve every time if you want to win your serve

see Nick Crossley's profile

Knowing how to hit a topspin serve could help you serve less double faults. The topspin serve helps you have good next clearance and the spin helps drop the ball into the service box.

How to hit the topspin serve: Your grip should be as close to the Eastern grip as possible. Then, toss the ball slightly behind you. If you missed the toss the ball should hit you on the head or graze the back of your head. As you strike the ball, brush your racquet up on the back of the ball, from 6 to 12 if the ball were a clock face. Continue brushing up and complete the swing by following through. Your momentum is going more up than forward, unlike a first serve.

Enjoy practicing this one, once you've mastered it, you won't regret the time you've put in.

see Mark Tiu's profile