Hi I just received my 24-70 F2.8 Nikkor lens. I am using it on my D90. Previously I have been using either the 18-105 VR (kit lens) or 70-300 VR without issues. However with the new lens (which is supposed to be a much better lens) I am getting lot of portraits to be out of focus. I am trying to shoot a lot of them at F2.8 to maximize the DOF. Particularly with photos with a group of people, I am getting the subjects out of focus. I am using single point focus aiming at one of the subjects, then recomposing and shooting. I think I am doing something wrong as lot of the portraits are out of focus.

Any help please...