When leaving a voicemail message, i try to make minimizing roundtrips the number one priority — i leave as much information as necessary to save the other person from having to call me back.

For example, if i'm trying to schedule a meeting with someone, just saying "call me back" doesn't help (if i miss their call, and they leave a message that says "call me back", we haven't gotten anywhere). So i describe my schedule and tell them to pick a time. They call back to confirm, and even if i miss the call, we're done, two messages max.