The less experienced the umpire, the less information they can absorb in a post-game evaluation. Take notes and as the game is wrapping up make note of the three biggest things and focus on those. Make sure to acknowledge and support the good things, too no matter how small or insignificant.
The more experienced the umpire, the more information they can absorb.
I don't know what your association requires but, whenever I evaluate someone, in addition to doing the post-game evaluation for the assignors, I also send my partner an email with our discussion bulleted.
~Dawg