This is a lot easier when you don't actually fancy the person you're flirting with. When you are deep in the throes of a sweaty-palmed crush, stringing together a coherent sentence can seem like a challenge. A good way of getting around this is to build confidence by practising on a neutral target - anyone from the girl who works in the corner shop to a friend you find vaguely attractive.
This doesn't mean showering your intended in compliments. Much of flirting is simply about making the person you are talking to feel good, from making them feel like they have your full attention, to emphasising the fact that you are enjoying their company. For this reason, the best flirts are often also the most charming people, able to win over people of both sexes with their conversational skills.
Check your body language
The adage that "it is not what you say but the way that you say it" is never truer than when applied to flirting. Good body language trumps smart chat-up lines every time. Don't worry if you aren't the hair-twirling, or chest-puffing (depending on your sex) type. Just listen carefully, maintain eye contact, and, most importantly, smile. Subtly mirroring the other person's movements, and occasional bodily contact – gentle touches on the arm to illustrate a point – also work.
Pick your moment
Bear in mind that there are times when flirting no longer justifies the 'harmless' prefix. While flirting at work can be OK, tread carefully if you want the person you are talking to take you seriously. As with so many things, men can get away with much more on this front, and are likely to be treated as roguish charmers rather than brazen hussies attempting to sleep their way to the top of the career ladder. Flirting with your friends' partners will also do you no favours.