It's not really designed for air cooling, so anything you do is sorta improvised.
I think part of it depends on which motherboard you are using. On some motherboards, you'll end up with a lot of cables getting in the way of the side fans which sit alongside the motherboard, which won't do a lot for efficiency.
If however, that section is clear, then you are probably best pointing the CPU cooler to the side so that it lines up (as best as possible) with the exhaust fan.
You can add rear exhaust fans, but I don't think it's likely to be necessary.