Summarize the following:
Springy, cushy carpet is great at absorbing sounds and frequencies in the room, cutting down noise significantly. Even several thick rugs can help keep noise down, and are an important step in soundproofing. Don't forget about the floor! Mass absorbs sound, and this thin sheet is made to absorb a lot of it. You buy it by the roll, which you then cut and apply to the walls, ceiling, or floor. Make sure that, as you work, you don't leave gaps between the sheets. This significantly decreases effectiveness. Cracks, seams, and exposed bits of wall and duct will all pull sound in from other parts of the house. Even if the wall or ceiling is already built, a little sound-proof caulking can close out unwanted noises.  Cover up wide or open door and window frames with an adhesive weather strip. Pay special attention to air ducts -- a lot of sounds often enter through them. Remember -- mass is your friend. Big, thick blankets on the walls will absorb sound from the outside much like insulation would on the inside. It doesn't always look great, but it will soundproof in a pinch.
Lay down a carpet. Purchase and apply mass-loaded vinyl to the walls and ceiling. Use acoustic caulking to fill in any air holes in the room. Tack thick blankets up to the walls for a temporary solution.