The general strategy for treating rooms an a budget is the use of fabric wrapped panels of rigid fiberglass or mineral wool like Owens Corning 703. The 2' x 4' panels are placed across all the corners of the room to tsme the room's natualr modes of vibration in the bass range which make the room's response drastically uneven. Also, panels are placed at the points where sound will take its first bounce off of a wall and come back to a microphone or an ear. Furthermore, the panels can be used in alternating fashion in parallel walls to reduce flutter echo. That's the very basics of it. Ask away if you have more questions.