The room you record and mix in has as much of an effect on your finished product as any of your gear and choosing a room to record and mix in can be very difficult. Sometimes, the choice is already made in the case where you are using a spare bedroom or office. If you have the flexibility to do so, try to pick a room that is not square, has higher than normal ceilings and is well insulated. The bigger and taller the room, the better. My home studio is in my 16 by 20 foot garage which is just over 8ft tall. The previous owner installed central air and heating ducts to the garage so comfort is not a problem except on those 100+ degree days we get in Northwest Louisiana during the summer months. I was able to scam a pretty good bit of carpeting so that took care of the concrete floor.
†††† If you are not so fortunate, there are remedies. Orienting your listening position in one of the corners of the room will help immensely. This keeps the sound waves from bouncing back and forth between parallel walls which can result in standing waves that will fool you into thinking that your mix is much bass-ier than it really is. If you can, hanging heavy drapes on the walls will cut down on reflections (many older studios were known to use surplus army blankets for both wall treatments and as isolation). There are also many commercially available foam products that are specifically designed to dampen reflections. If you should decide to use a non-commercial product, make sure that it is fire-retardant. Cardboard or plastic egg containers are excellent at scattering reflections but extremely flammable.†
†††† In a tracking/mixing room combination, you want to strive for as neutral a space as possibleónot too live (lots of reflections) and not too dry (no reflections). There are tons of books written about this subject and you can get as detailed as you want but donít go crazy and do something thatís not easily reversibleóespecially in a bedroom or interior space. NonĖ reversible but effective solutions include another layer of drywall on all the walls or actually building another room inside the existing room that is isolated from the outside by using special construction techniques and products