This is one of the reasons why I don't like doubles as much as singles, I have to be a freaking psychologist on the court. Some people don't like to take direction, some people need little cheer-ups, some people get thrown off by tactics by the other team, and some people get all mopey after missing a shot, or all of the above. Are you that mentally fragile that you need little pick-me-ups during play?
With that in mind, I try to keep everything simple with regard to communication to my partner. I try not to get mad at my partner, and give general encouragement ("Nice shot!"). When it comes to strategy, I'll say some general things, like this person is aggressive at the net, lob over him, or this person doesn't like slice, or this person's backhand sucks, or hit all balls at this person. But I won't say "Lob your service return", or "slice to his backhand", because my partner may not have those shots. Can't get blood from a turnip. My partner just has to hit the best shots that he can.