[chasw98]

I've seen Bryan give very good advice on many occasions, so I would listen to him. My thoughts would be:
01) Do the mirror trick and use absorption on the first reflection points on the side walls.
02) Look into some form of diffusion for the rear wall. (A bookcase with different sized books can some times work effectively).
03) Take care of the first reflection points on the ceiling.
04) Bass traps. You can rarely have enough. I mean true bass traps that will absorb the deep stuff, usually very expensive and bulky even doing it DIY.

All of these suggestions do not include any WAF problems, but in reality you usually have to compromise. If you are serious about it, measure, measure, measure, both before and after and at different listening positions. What may sound good at the sweet spot might not sound very good 2 seats over or behind. Back in my day, everyone strove to build an LEDE (Live End Dead End) room and as time has gone on the buzz words are now RFZ (Reflection Free Zone). These are types of environments you would find in studios more than home theaters but the concepts hold true in general. Do some googling on DIY absorption or acoustics and start getting some ideas. It can be done quite effectively and relatively inexpensively if you put your mind to it.

Chuck