btw, Low hanging fruit is very clear, it's been stated here and many-many other acoustic forums:
1) Pick RFZ zone as your small room acoustic model, it's the easiset for DIY (IMO); front sound stage specific ; I've not seen surrounds addressed specifically in the various small room acoustic model's ....
2) Broadband bass traps in corners, big ones if possible, 34" x 24" x 24" (use pink fluffy for that size). Soffit style on wall/ceiling is also.
Plan to cover them on room facing surface with thick kraft paper or 6mil plastic to reflect the mid-hi freq back into the room. Fabric cover over that.
3) Using mirror trick, plan where your side wall 1st reflection treatments could be
.....If you want to use measurement and verify exact placement, use ETC and the techniques discussed for ID/placement.
.....If not, using just mirror trick, you may over dampen slightly, or may not get all the reflection points, but definitley improvement will be heard (the 90/10 rule)
4) by the book for side wall treatments, 4" OC703 + 4" air gap is best to even absorption thru the freq spectrum 250hz and up, again 16" of space may not work for some, 2" + 2" air gap will leave some of the lower freq not addressed.
>>Trade off time for the customer to decide
5) Using mirror trick, plan where your ceiling 1st reflection treatments could be....same comments as 4) above.
Listen and enjoy them
Better is measurements, but many don't want to shell the $225 or so for measurement mic/gear and learn the software.
Not hard, but just one more thing in a busy life.
I see some are asking for a "Plan...do...check....act" cookbook approach.....
Looking at this link, everyone can see visually the various small room models, it's 7 pages from the book "Acoustics and Psychoacoustics Applied"http://eetimes.com/design/audio-desi...n?pageNumber=0