As others have said.  A big sturdy tripod with a quality head are a big help.  Then it possible use a remote to fire the shutter.  You also want to look at ways to dampen motion.  One way is to hang a weight from the center of the tripod.  Lots of shooters will just hang their camera bag.  You can also try laying your non-shooting hand on top of the lens to dampen motion.  If your body has a live-view type feature you may be able to use that to fine-tune focus, especially if you are using a shallow depth of field or in my case a manual focus 800/5.6.