Many times a player will make their shot selection way too complicated, especially in doubles. When you are playing doubles and you are returning serve, approaching the net or hitting a groundstroke, try this. Keep your vision focused on the ball; let your peripheral vision track your opponent's position. If the opposing net player is stationary, go crosscourt. If the opposing net player moves out to poach, go up the alley or behind the net player. If the opposing net player is standing too close to the net, lob over him or her.
Remember, you do not have to hit the ball to beat both opponents. You just have to beat the closest player to you. Once you get the ball past the "up" player, then work on beating the "back" player. This way your partner can help you. Doubles is a game of "under and over." When you feel an opponent coming in to attack you, hit the ball under them or at their feet. When your opponent is too close to the net go "over" them or lob. When you get the ball under your opponent, get ready to attack by moving in. If you, by accident, hit the ball too high, stay back and defend.
Do not make your strategy too complicated. Stop planning where you are going to hit the ball before the point starts. You must wait until you get more information. How tough is the shot? Where are your opponents? Where are you on the court? Let your opponents' position be the number 1 reason to determine where you will hit the ball. I have many players that have beautiful strokes, but cannot translate that into "wins."
Compete against your opponents, not the court. Do not judge your shot's success by how close you hit the ball to the lines. Do not judge your shot's success by how high or how low it is to the net. Instead, under or over is a better approach. Look at the ball, feel where your opponents are, do not look at the net.
Good luck on the courts!