little help with speaker placement

[codehorizon]

I'm trying to find out the best placements for my 5.1 surround speakers. I have some photos on my ht tab for a reference. I have tv stand on my front wall with subwoofer on top, and one front speaker just to the left of the stand, while my other front speaker is to right of my desk. My center speaker is on the top shelf, above my PS3 in between the two game boxes. I also have both rear speakers on the back left and right wall, on opposite sides of my bed. But I don't get the effect of surround sound. What are the best placements to get the surround effect? Also, any rearranging tips/advice/feedback about my setup is welcome.