Do you have a picture of the room?
Not sure what you are asking but I would use a corner desk in that space, small file cabinet and a couple of small or wing back chairs.
Pictures would help. That way we can see door and window placements.
One way to get a little more floor space in a room this size is to reverse the door so that it opens outward, instead of into the room. Depending on your layout, this may facilitate furniture arrangement.
I would try to place the desk in the center of the room so that everything isn't against the walls.