It would depend on which one it was.
If I met Shatner in real life, I would ask to have a picture taken with him.
If it were Jeri Ryan, I would ask if she wanted to have a drink with me. ;)
Same thing I've done all along, shake their hand, introduce myself and talk to them like a normal person...
That's how I've gotten to meet/talk to Walter Koenig, Jimmy Doohan, George Takei and Michael Dorn...