In doubles, position on the court is very important. Many times you will lose a doubles match and think, "I lost, but I played OK and I made just a few errors." In reality, you were constantly in the wrong place at the wrong time. You were not in position to even hit the ball.
What to do?
Remember, in doubles 80% or more of the shots go crosscourt. Worry more about the middle than the outsides (alleys). Never stay in the same position two shots in a row. Move your position on every hit, not just after you hit the ball, but also even after your partner hits the ball. Follow your team's shot, commonly called "shadowing" or the "wall theory." In the wall theory, try to keep an imaginary 11-12 foot bungee cord between you and your partner when at the net. If your partner hits a great offensive shot move toward the net to attack. Keep changing your position. Keep your opponents constantly guessing. The movement is fun, very cardio and keeps your opponents off guard.
Take a lesson on just positioning. When your partner knows where you are going to be and where you are going to go, the tennis is more fun and you won't be out of position.
Good luck on the courts!