You can turn the closet into an enormous bass trap if you want.
You don't want to be seated in the middle of the room.
I'd set your desk the way you have it in your picture but a bit closer the end wall (opposite the door) so your ears are somewhere between a third and half the length of the room from the end wall.
Blankets and the like will only cut high frequencies. They'll sound like there doing something useful, by deadening things, but they may do more damage by screwing up the frequency response of the room more than helping it.
With the desk like it is, you need 4"+ panels on either side of you on the walls to absorb the early side reflections.
Have someone hold a mirror on the wall and with you sitting at your desk you want to see your monitors in the mirror. Then hang a bass trap there. There's also a reflection coming off the ceiling for which you can hang a bass trap above you. Try and avoid reflections off a large desk.
You can hang a panel on the back of the door when it's closed.
As mentioned, the corners are where to start for tackling bass/low mids. You won't be able to do much about real bass.
This forum has everything you need to know and a bunch of people more than willing to help. Also an enormous amount of info on making your own bass traps. Just provide your drawing and room dimensions if you post.
You can use the fantastic, free
Room EQ Wizard to measure your room's response before, during and after treating it.
There are a lot worse rooms than yours. Enjoy it.
post edited by Paul P - 2013/04/07 15:46:30