Summer is a great time to try out stuff you wouldn't normally do. Try a different approach to handling an irritating coach. Talk to players more. Try working wider or closer in at L. Try moving more or less at T. Try being bigger or smaller. Try to appear more deliberate or relaxed. Try out that super cool quadruple tweet thing you heard somebody use. Let 'em play more or tighten up more, and see what happens. Find a kid who lacks confidence and try using your demeanor and a little humor to give him/her a boost. Work on your partnering skills and focus on making a weaker partner better. Talk to a parent or two between games and ask them about their kid. Try working without a lanyard.
The idea is to stretch yourself in new ways and directions. If you make mistakes while doing it, it's only summer ball and nobody is going to care that much. If you don't make mistakes, you're not trying hard enough.
All this assumes, of course, that you are already capable of calling a decent game and don't really have to focus all your energy on reporting mechanics or calling travels.
Just my $0.02