Try slowing down. You'll be surprised as to how much control you will have. Develop consistency by trying to hit more than one or two shots in a row. In practice, rally with you partner for four or five shots before you are allowed to go for a winner. Try to always be one shot better than your opponent.
Depth is the name of the game.
By hitting higher over the net, you will minimize your net errors. You will apply a lot of pressure to your opponent who will be faced with a high forehand or a high backhand. We all know how difficult these shots are. Finally, begin to hit with power. If you develop your game around power, it is always at the expense of control, consistency, and depth.