Essentially I think it boils down to this:
- Be prepared before coming to rehearsal.
- Don't waste too much time getting setup or dialing in the perfect tone.
- Once you start playing, keep chatting minimal and on topic (about the song you're working on).
- Work your way through your list of songs until you have them all down, then start again at the beginning.
- Take time where needed to correct problems and mistakes, but realize that some things just need time to be worked out alone (see #1).
To be prepared, you all have to practice. Usually this means listening to and playing along with recordings. Make sure everyone has a recording of the songs. CD or tape copies, youtube links, mp3s in a dropbox folder, etc. Using dropbox works really well, because if there is any change in band members, you just point the new people to the folder.
If you're still working out new tunes, or arrangements for covers, you can work these out without the drummer. Record them and send recordings to the drummer. You decide whether to use your regular rehearsal time, or meet separately at a different time.
Jamming endlessly is not very productive, obviously. But starting the rehearsal with maybe 10 minutes of jamming is nice for a warm up, encourages improvisation, etc. It's not a bad idea to record these, might come up with new song ideas!
Also, trying to play just certain parts of a song to save time can sometimes take longer than just playing the darn thing all the way through! And playing all the way through helps you with memory.