Of course, you should also mount the camera on a tripod so that camera shake caused by handholding the camera doesn't create blur.
You can take advantage of mirror-lockup shooting only in the P, Tv, Av, or M exposure modes. Enable it through Custom Function 10, as shown here.
Mirror lockup eliminates the chance that mirror movement blurs the photo.
Mirror-lockup shooting requires a special picture-taking process: Press the shutter button once to lock up the mirror, release the button, and then press it all the way down again to take the picture.