The newest high-end DSLRs offer a function that allows you to fine-tune how each lens focuses on your camera. There are lots of instructions and aids available to accomplish this task, some more effective than others.
This is one of the first things we do whenever we get new camera bodies. Until you’ve done this, you can’t be sure your camera and lenses are perfectly adjusted for each other. Depending on the number of lenses you have, this might take from 15 minutes to. A couple hours… But it pays off big time!
Here is Canon’s helpful guide to how your autofocus system works, and explains shooting techniques for proper use as well as how to do the adjustments: