The game of doubles in tennis is a far more complex game than singles. In singles, players can be much more one-dimensional and still be successful. Top singles players can do quite well with only groundstrokes as a weapon or with just a big serve. In doubles, you need to be able to return the serve with consistent precision, volley well, place your serve to set your partner up, etc.
There are four videos below that were created by Bob and Mike Bryan who have been the most dominant doubles team in the history of Open Era tennis. Although the videos contain extraneous material you may want to fast-forward through, their intention is to correct long-standing mistakes that they consistently see being made by recreational players. Unbeknownst to many fans of tennis, touring pros often play in exhibitions or “Pro-Ams” in which they are paired with amateur players. They also have identified similar mistakes that players make at both levels.
Just an FYI that although these videos are designed to help your doubles play, the second half of the fourth video has a bit of a sales pitch for a more comprehensive course they are promoting. The third video is not from the original series, however it has some great material in a condensed form.
Hopefully these videos will help you to improve your doubles play and gain the most out of your time on the court.