When my husband and I play tennis - we make sure to be complimentary and kind. We uplift each other with encouraging words. And in the rare events when one of us criticizes the other - we quickly kiss and make up!
We are obviously always trying our best - so if one of us is not playing well it's not on purpose - and what we have learned is that by accentuating the errors and trying to coach the other one - causes them to play even worse!!! It's best to just unconditionally love your partner - and know that they are doing the best that they can in that moment!