All too often, players (including myself) identify the handedness of their opponents too late—after a few points have already been lost. So, as soon as you step onto the court, be sure to identify whether your opponents (as well as your own partner!) are right-handed or left-handed.
Once you identify who is right-handed and who is left-handed, be sure to be aware of where they are on the court before every rally. In other words, are your opponents’ forehands in the middle, or are their backhands in the middle? What about you and your partner—are your forehands or backhands in the middle? Share this information with your partner and communicate with each other if and when it changes. Constantly remind yourself and your partner throughout the game.