Make sure my bowels are evacuated, have one bottle of beer, have two bananas (an old drummer friend of mine said something about natural beta-blockers, that reduce the adrenaline uptake/effect, actually I just like bananas) and compulsively check my cables are all wired up correctly.
Also spend most of my time reinforcing to the sound engineer that under no circumstances is he to shoot Phantom Power back up his lines at my gear.