The right attitude and appearance count a lot in flirting. Before you go out, get yourself into a relaxed, social and outgoing mood. Be positive, but realize that there isn't much at stake. You might get to make a real connection with a guy, but if you don't, there will be plenty of more chances to flirt.
Get your appearance and body language right for flirting. Being clean, well-groomed and attractively dressed will make others more likely to come up to you. If you don't feel confident, fake it; hold your head high and keep your spine straight, but relaxed. Smile and feel at home in the space you are in.
Approaching someone is one of the most difficult parts of flirting. Pick-up lines rarely work; if you want to really make a good impression, you'll have to use your observational skills. Cruise your target and observe what he's wearing, what he looks like, what he's drinking. Then, give him a compliment. Tell him his glasses look good or you really like his smile. It may seem cheesy, but it can really get a conversation started if you come across as relaxed and sincere. If you get him talking, ask some questions. People like talking about themselves and enjoy seeing that their conversation partner is interested. Have some follow-up questions or observations prepared in case conversation stalls, but don't use them if conversation seems to be flowing on its own.
If you are in a new place or somewhere out of your comfort zone, try making it work for you. Approach someone who looks more comfortable, someone who looks like he belongs in the particular bar, club, coffee shop or wherever you are, and tell him you're new at the place. Ask him some questions about it, such as what's good to order, whether this is a typical night or whatever else occurs to you. If you've guessed right and he's familiar with the locale, he may tell you about the place, show you around or talk about his experience there. If you were wrong, you can share your observations about the place to start a conversation.
Tailor your flirting to what you are looking for. If you'd like to find a date and maybe explore a relationship down the line, keep the innuendo light. If you're looking for a hookup, it's OK to be a little more aggressive; if he's scared off, it wouldn't have happened anyway, and if he's interested, he'll reciprocate. Whatever your designs, use body language to indicate your interest. Make eye contact and smile playfully, touch him lightly once or twice at appropriate times during the conversation, such as when he makes a joke and otherwise show that you like him and are interested in him.