Here are a couple things to get you started.
1) Make sure your monitors are firing down the longest wall. You would be facing the shortest wall.
2) Put your mix spot (where you sit) 38% of the room length.
3) Treat as may corners as you can with bass traps that use rigid fiberglass or mineral wool.
Check out
GIK Acoustics - Education for room set up and how acoustics would work within your room.
Glenn