Best is lots of dryfiring, concentration.
Even then you'll get "pre-match" shakes.
I get them mostly in Off hand because its my worse position and it's normaly the first stage you fire.
One of the best things that works for me, and those team members I've coached is, just before the match, set on your shooting stool, (or chair) and relax as best you can, the lean over with your head in your lap and take deep breaths, hold it in as long as you can, Let it out, and try to wait before you suck in more air.
Do this three or four times. Then just set there, totally relaxed for a few minutes.
Get a hold of the USAMU Pistol Marksmanship Guide and/or the International Rifle Marksmanship Guide; they both have excellent excersizes for controlling shakes and other aspects of mental conditioning. Both books are $6.95 each from the CMP Bookstore.