As a few people have said start with something foolproof, that you can do without thinking about, and before you know it you're in your routine and the nerves have subsided.
I'm really bad for suffering from this as well, although I'm sure it feels worse to me than it looks to spectators. It's known as an adrenaline dump, when your bloodstream is flooded with adrenaline in a short period of time, bringing on the shakes, sweating, loss of motor control, the mumbles etc.
If it really is hindering you the best thing you can do is breath deeply, breathe in through your nose for a count of four; hold your breath for a count of four; exhale through your mouth for a count of four; hold your breath for a count of four, and then restart the cycle.
Breath deeply and methodically – completely filling and emptying your lungs during each cycle. This will lower your blood pressure and stress level, and minimize the overwhelming side effects of an adrenaline dump.
Alternatively, just have a few beers beforehand.
