Sit in your optimum listening position and place foam at all mirror points between your head and the speakers. The idea is to have the foam at all first reflection points. Both side walls should take priority, then the wall behind your head and the ceiling. If you have enough, doing the wall behind your speakers is a good idea too. Note that this will do absolutely nothing for bass - you would need bass traps in the corner of your room to deal with this. There's a really good sound on sound article on room treatment - worth having a look for it.
My monitors are in a terrible place. This is kinda mostly for helping the recording in the middle of the room, but yeah, would probably be a good idea to sort the monitoring situation out too. I figure no matter how good the monitor situation I can't polish I turd that's badly recorded!
I'll go check SOS. Cheers for the tip.