You can use the candle or lamp technique to if you have any first reflection points on the front wall (check before you laugh).
A lot of people will put them in the center of the front wall (often, there's an equipment rack there).
Then, I'd use them to make the room symmetric (if necessary)--I mean if you have absorbers on the back wall (say, an LP rack), then I would consider putting a panel on the front wall symmetric with it.
No expert, but that's my approach.
