I would have it pointed so it moves the leaves a little on each plant. Blowing either across the tops or through middles to make sure the air gets pushed around. Of course it all depends on how many plants, density, rh%, etc... Sawneys idea isn't bad either.
I have a static fan that is mounted high and blows air around above my light and then oscillating fans down below. It's a 4x4 so lots of room and air that needs to get moved.
I am probably going to install several computer fans for upcoming grows for constant air movement. They are rated for a lot of continuous useage and the "silent" versions are nicely quiet.