I used to coach my partners. A lot. During a match. Uninvited. It didn't go well.
At first I was confused - I was trying to "help" them play better! Why would they get upset?
But then - someone coached me. During a match. When I didn't ask for it. And you know what? I got upset too!
So now - I focus on playing my best - and strategizing with my partner about the OPPONENTS WEAKNESSES - and life is much more peaceful and fun on the courts!