Rear channels or surround channels? Surrounds should go to the sides and just behind the main listening area and maybe a foot about ear level or higher as need be.
Rears should be in from the sides to help to fill the gap between the side surrounds. Same goes for height of these.
And just adjust as you need to for cosmetic or other reasons. If you are using something like the QS speakers from here, they are GREAT for being forgiving on their exact placement.
Here is an article from this web site that gives much more detail. I've seen the exact graphics elsewhere too, and they are as legit as gold. Home Theater Layout
M60s, VP180, VP150, QS8s, SVS 20-39PCi, HTPC, JVC RS45, Onkyo TX-NR709, Shakers