Oz hit on something that deserves some more discussion. In addition to breathing, there are some basic physical relaxation techniques that you can use.

When we're tense or straining we pull our shoulders up tight, clench our jaw and tense our neck. Concentrate on relaxing your shoulders, and jaw and letting your neck go limp. With deep breathing (through your nose, full, deep breaths) this will help open up your body and relax you.