First of all, your desk must be centered in front of the top wall (the 8,8' one). The room will be way easier to treat if your desk is placed in front of one of the smaller wall of your room (and not the larger one).
Then, cover all reflections points: sit at your listening position and tell a friend to hold a miror on one of the wall. Tell him to move the miror until you see one of your monitor: mark that place. Do this for both monitors on all walls (including ceiling): these are your reflection points. So, you should have at least 10 absorption panels to place on your marked spots (the most important ones are the ones on your side walls and ceiling).
Finally, cover each corner with bass traps: if you can afford it, place the more bass traps as you can (cover all 12 corners (4 wall/wall, 4 wall/ceiling, 4 wall/floor)). If you do not want to cover all that, you can only cover the 4 wall/wall corners (it should be fine).
P.S. If you want to be sure if your new acoustic setup works great, see if your mixes translate well on other systems or buy a measurement microphone (like a Behringer ECM8000) and make some test with RoomEQWizard. If you want further information, go check the acoustics articles/videos on RealTraps (Ethan Winer) and GIK Acoustics (Glenn Kuras): all I told you was taken from here.
Hope this helped!