That depends on the type of nervous.
If it's "around-people-nervous" I tend to become shakey, and I start sweating. To calm down, I try to get the talking done, and I also stim.
My stimming in this kind of situation is mostly like: Drumming with my hands (On my legs and sometimes on tables), constantly wriggling my toes, "foot-flapping" (like hand flapping, just with the feets).
If it's nervous about something that is going to happen, then I can be alone in my room, and then there are far more stims. Like hand-flapping, turning around on the chair, sometimes a bit rocking, putting my hands to my mouth (well, sometimes I do this in public too).
Of course, these stims are not limited to when I'm nervous, but are also apparent when I'm excited.