Every week I'm responsible for running two practices for my church (I'm music director for Trinity Church, for those of you that don't know). Here's 5 keys that I've found to running an effective practice session:
1.Start on time
It's hard to do with musicians, but starting on time is one of the biggest keys to an effective practice. You'll not feel rushed the rest of the rehearsal, and you'll be able to manage your time more efficiently. If someone is repeatedly late, confront them privately about it. They need to know how important it is to be on time so they don't waste the rest of the band's time.
Note: make sure you end on time, too. If you make people stay late, you're not respecting their time, and they probably won't respect your time in return.
2.Play all songs all the way through
So many bands will play a section of a song over and over, and never get the feel for how the whole song sounds. Make sure that you run through the whole song, even if it's rough- you may find issues in the song you never knew were there.
3.Work on trouble spots
Once you've done a full run-through of a song, don't be afraid to loop sections that need work. Spot-practicing will tighten up the group in a way that nothing else can.
4.Break it down
They did it in high school band, why not do it with your group? Single out a few musicians that are not as tight with the rest of the group, and have them play their parts together. It'll make them practice harder at home, tighten up the sound of the band, and challenge the entire group to listen to each other more effectively.
5.Do a run through
Walk-throughs of your set are an essential part of any practice, and will make sure everyone understands all of your song transitions. If you don't have time to do a full run through, just play a few measures of the beginning and end of each song.