Home practice can be a pain in the ass coz neighbours tell you to keep the volume down all the time, and who of us haven't had a police officer knocking on their door and asking them to keep the noise down? ... sound-proofing your room/ garage is crucial sometimes especially in quiet neighbourhoods.

Anyone who has his room/ garage sound-proof can share their experience in here, keep in mind to mention:

* The space you sound-proof (Room, Garage, home studio)
* The technique used (double walls, hollow bricks, foam, double-glazing)
* The materials and tools you used
* Aproximate budget
* Step-by-step installation (or if you've had a company do that you could mention its website)
* The problems you faced, and the end result

Sounds like your looking for room isolation and, not treating the room's acoustics. The key to room isolation is density, you're going to want to use a dense material that keeps the low end frequencies from escaping the room. I imagine it would be fairly expensive to treat all four walls in this case but, using dry sand in some sort of containers would work. Or if you can afford to build on some thicker walls you could build some new frames, fill it with a thick fibreglass insulation cover by drywall.
Aside from that, you could just go with some strategically placed bass traps (usually made out of wood frames with fibreglass insulation wrapped with a cheap fabric) to soften the blow of the bass amp and bass drum. The whole foam and egg carton method won't be of much use, as that's only good for high frequencies which, is a lesser concern.

Did a "room isolation" search for ya on a home recording forum I attend, normally I don't think any one can do a forum search without signing up - though it's a great place to learn all aspects of home recording. Here's the search result link though Room Isolation Search

Well,where to start?
First its quite pain in the ass to sound-proof any space,but if you want to do so I can recommend the following solution:
Sound-Proof your room by using the cardboard boxes....This require not just any box but the the one in which are stored eggs .Procedure is simple.Just glue on these boxes on the walls of yours room (future practice room).If you done this right ,you'll have no longer neighbours related problems.