I always understood flirting to be promoting a romantic or sexual encounter or encouraging the advances of others by chat or a knowing smile, or a wink just for instance.
Flirting for me is the confidence to chat amiably to any member of the opposite sex. There are degrees of flirting but you are wasting your time if the person you are trying to flirt with does not think along the same lines. Most flirting would be of a complimentary,very mildly sexual,double entendre or humerous nature. Stay on the safe side until you have made a few 'saucy' comments and see how they respond. If the banter is well received you can go as far as you feel safe with. I always think that a bit of banter and flirting brightens up the day of many people, shop workers for example. There are too many miserable B's out there.
Smooth1
Fun, better if its welcome though. Part of the build up when meeting someone new to flirt at I say
J
A subtle sexual overture. The subtler the better.