This may sound weird, but a Veteran Bodybuilder taught me to visualize myself standing on a perforated piece of paper, press down on the paper with the ball's of your feet, and try to tear the paper down the center. It'll bring out all the separation in your Quad's. Practice this enough and you'll always be tight on-stage.
Another tip is if you begin to shake while holding a pose, just open your mouth slightly and the shaking will stop. I don't remember how, but it works.
Good luck,
Chuck