I've found in my gaming group that the guys that start to choke their dice whimpering "I'm not gonna make it. I'm not gonna make it!" tend to actually fail their rolls more often than not.
So my thinking is it's best to clear the brain from any thoughts like "If I miss we're dead" and just step up and roll that sucker!
Or, if that doesn't work, throw the dice as HARD as possible so it bounces of everything; that way if it's a fumble you can always blame the wall, gaming buddy, GM shield, your dog, etc.