When I was younger I was quite the flirt! I would smile a lot, laugh at his jokes, touch his arm or shoulder a lot, tilt my head to one side when I talked to him or listened to him, and really look at him with adoring eyes. Hope this helps.
If she seems to be flirting with you, flirt back cautiously. At work, you have to be careful because your actions could be misinterpreted. We know of people complaining of sexual harassment. So, observe. Proceed cautiously.