If you are willing to put some time into this try the Sumiko Master Set method for speaker placement. Another option is the Audio Physics method that is best used with the long wall placement suggested by Nvp. Your room appears both wide and deep enough to try this method. Of course other logistics and room configuration may prevent this, but it is well worth trying if you can.
I have used both these systems, individually and in combination with great results.
I have used both these systems, individually and in combination with great results.