It really depends on the lens you are using. When I've got my EF 100-400mm @ 400mm the camera will autofocus pretty easily. I also like to focus via Liveview with the 10X zoom, that really helps. I find the camera sometimes has a harder time with the exposure level (Again all depends on the situation).
I always like to use the rule of thirds, I try not to place the subject right in the middle of the pic (At least in POST, during my actual shooting I really don't care, lots to crop out)