I was looking for some focusing tips via Google the other day and I found this one to be of somewhat help. I will be trying it out.
Q: I noticed you have many photos of more than one subject/person. In each case, both people are perfectly focused. Is this optimized by having people close together so that the camera is focusing well in the middle of them? If you had two people who were not close together, is the best way to keep them both in focus going to be with lots of light that enables a smaller aperture/larger f-stop? What if you are indoors? Is lighting the key?
A:Depth of field (the range of an image that is acceptably sharp) at any distance is determined by a combination of focal length and aperture. Wide angle lenses and small apertures (f32, f22) give the greatest apparent DOF.However, the closer the subject is to the focal plane of the camera, the shallower the depth of field becomes. The final piece the puzzle is that the depth of field extends further beyond the true point of focus than it does in front of it... that means, in practice, if you want 2 objects to appear sharp, you should focus at a point past the nearest object 1/3 of the distance to the farthest, using the smallest aperture (largest f number) available at the shortest focal length suitable to fill the frame. Easy!