Is it in a basement? Or something like a freestanding shed in your backyard?
Acoustic Treatment: things done to the inside of your room to make it sound good.
Acoustic Isolation: things done to the wall of your room to prevent the sound from escaping.
When dealing with acoustic isolation it can get expensive quick. Your friend is dead air, and mass. You'll want to build a room inside a room, with lots of dead air or mass in between.
This usually includes building a floating floor and two sets of walls. For the floating floor, some people have had luck using old tires on the floor, then stuffing them with old clothes, then building a floor on top of that. Daptone Studios in Brooklyn has gone this way (Amy Winehouse, Sharon Stone etc.)
Jack Johnson environmentally friendly all-gree studio uses old jeans stuffed between the walls.
These might not be the right ways to go about it, but theyre ways that some big studios have used in the past. Im sure someone is gonna step in here and probably negate everything I told you, so take it with a grain of salt
Mike