The place my band practices is basically like a single car garage with a loft.We share it with 3 other bands (one band practices up in the loft, all other 3 practice in the lower area). One guy drums in two bands and he lets my band's drummer use his kit. We share guitar cabs, but people bring their own heads. The bass players have their own rigs. We practice in the covered section (all walls have carpet and foam on them) with the drums at one end, and guitar amps pointing towards the drummer. The bass rig is usually over nearby the drummer and the PA has one speaker pointed towards the drummer, bassist, and pretty much directly at the keyboardist (for the one of the bands - she requires that she hears herself at all times). The other pointed in the opposite direction towards the guitarists.
Our practice space is actually a storage rental space in an industrial park with metal walls. Like I said, all the walls have carpet and foam. If you can't afford that sometimes hanging heavy blankets helps dampen the sound.