To pretend one won't be nervous before an important performance is to deny normal human nature; this is especially true if a long hiatus exists before one's last gig. There is, of course, no substitute for practice, practice, practice. Know your program backwards and forwards, because at an actual performance, we all play less than perfectly.
Beyond that, I like to make sure I've eaten something about two or three hours before the concert (never just before), and that I've exercised earlier that day.
20 mg of propanolol, a beta-blocker, (brand name is Inderal) is a popular way to curb performance anxiety--without any substantial side effects other than a slow heart rate, it puts a lid on one's adrenalin. It can also, unfortunately, put a lid on one's fire and emotions. Coffee--the opposite. A real enemy. Drink a couple of cups of Starbuck's before a concert and just watch your fingers shake!
The best way to curb the nerves, though, is to practice and perform a lot.
Good luck!