As someone who GMs and plays;
1. Work out a schedule that works. I have a live group I play in that meets bi-weekly. We play for about six hours, give or take. I am also part of a VoIP group that meets weekly, and plays for about four hours. And lastly, I GM for a VoIP group that meets weekly and runs for about six hours. RL will interfere, don't worry too much about that.
2. The group is, as a rule, yours to command - which can often mean you sit back and let them run off with your plot. Take notes. Take /lots/ of notes. And then have it all come back to bite them in the bum. They like that.
3. What Aleph said.