Magic should be approached from this standpoint. If you are being paid to perform, than you need no introduction. You are there for the entertainment of the guests and your presence is already generated.
However, if you're looking for an impromptu situation, such as the popular street/guerilla style of magic, than you need to find and in. People are you're best advertising. If people have seen you before, than they might bring it up. You have to find that in though. Just coming out with, "Wanna see something cool?" Come on. We're performers. We have to weave the web of distraction. Set and size them up. John Bannon follows the rule of three. They have to ask him three times to see something. He wants them to want it. And sometimes saying no is your best bet, This builds the suspense. Eventually they will be begging you to perform (sometimes bringing a deck of cards!). Intruding can make the magic awkward. And a little corny. If I want to perform, it's because I see a link to the group and feel that my performance would heighten the evening's events, and make the group have fun. Not just to showoff. Remember the old Cardini addage,
"A man in a magical world...."
Regards,
Jonathan