Once your team has served, stay back for the return shot. Once you or your partner returns their shot Move up quick! Too many newbie players stay back deep - even when their opponents aren't pressuring them to stay back. You have the advantage up at the NVZ (kitchen) so unless the other team is keeping you back at the baseline with long hard drive- you want to be near the kitchen.
Too many beginners hang back, and even worse start to come up and don't commit- they hang out in "No Man's Land" in the middle. We've talked about this before - that's the worst place to be.