To go along with the caffeine thing, if you are a regular caffeine drinker, (ie coffee in the morning, soda, etc...) then don't stop drinking it right before you shoot, unless shakes and splitting headaches are something you enjoy.
I drink a lot of caffeine, so at a tournament, don't be surprised if you see me with a coke or caffenated drink.....
Your bow can't be too heavy for you, and it should be balanced so it is at "zero balance" like GRIV says. He likes his bow so when he shoots, it doesn't tip or anything, it just sits in your hand.
Too much holding weight can be a problem too. If you need to use a lot of arm muscle to hold the string back (instead of relaxed and using your back) then it is too much and will cause unsteadyness.
Too weak of an anchor point can be a problem too. Have someone lightly tap your release hand at full draw. If it causes sight movement, you need to have a firmer anchor point.
Too wide or narrow of a stance can cause some problems too. Experiment around. I like to set my stance, aim, close my eyes for 3 seconds, open them, and if I am not on target still, then I adjust and keep experimenting until my sight stays on the target after I open my eyes.
The way your bow arm is can cause trouble too. Too much of a bend, or too overextended of an arm can cause unsteadiness. Relax your arms casually at your sides. That is how your bow arm should be.
DRAW LENGTH! One of THE most important factors of steadiness. Too long of a draw length and you will never see the sight stop moving, too short of a draw length and you will see a stop in sight movement but will have sudden hurkey jerky movements. Tweak it until it feels just right.
Body posture. If you are leaning backwards, that takes the tension out of your back and puts it in your arms, taking out the "dynamic tension" in the shot and throws things out of wack. You want to be straight up, and relaxed.
Too high powered of a scope. If you are perceiving a lot of sight movement, sometimes that can freak you out and cause all sorts of trouble. If you are just starting out with a target scope, start with a 2 or 3 power and work your way up.
Thats really all I can think of right now...