Choose a large closet or a small room to convert into a soundproof booth. You can also frame out a section of room to accommodate a soundproof booth using 2 by 4's and drywall or plywood. Use screws to hold the drywall or plywood in place. Avoid any electrical outlets and light fixtures. Install a solid core door.
Install Styrofoam insulation panels on the walls, ceilings and the back of the solid core door using a hammer and finishing nails. Measure the Styrofoam panels with a measuring tape and cut the panels with a sharp craft knife. Make sure that each piece of Styrofoam insulation panels is butted next to each other as this will prevent the "leaking" of any sound from the booth.
Cut a hole for the doorknob with a craft knife and check to see that the insulation panels do not prohibit the closing or opening of the door.
Cover the Styrofoam panels with carpeting for additional sound insulation. Cut and place the carpeting pieces wrong-side out so that the back of the carpet is showing. Attach with a hammer and finishing nails.
Cover the floor with a piece of carpeting if there is none. Place the carpet right-side up as you would normally lay carpeting.
Make a test recording in the new soundproof booth. The sound should be barely audible from outside the booth. Check for any reverberation.