Don’t Stare
So you’ve spotted a girl and you want to go for it.  Here’s your next tip: Don’t stare.  Your goal is to convince her that a connection between the two of you has happened by a glance and that the glance occurred when both of your eyes met for the first time.  Obviously you’ll need to time that moment well, but you don’t want her to think you are or have been staring at her.  Be subtle with how you watch for the moment when you can create the ‘instant connection.’  The trick is to look at her with your peripheral vision, look away the moment you notice she is about to look in your direction, and then to look back almost immediately and then lock your eyes on hers to create the ‘I just noticed you’ moment.
Show your interest, then look away.

Once you create the ‘I just noticed you’ moment, fixate on her eyes for a second or two longer than would normally occur as a glance, just enough to let her know you’re interested.  Then look away immediately.  Again, you don’t want her to think you’re a creep, and if she thinks you are staring, it will do exactly that by making her feel uncomfortable.

Well, almost.

There are times when you are better off not flirting and there are places where you’re better off not flirting too, if for no other reason than the odds are stacked against you at those times or in those places.
Flirt with honor
Clearly, you don’t want to be flirting with a girl who is out on a date with her boyfriend!  Even if you do and think of yourself as someone who isn’t afraid to get into an altercation with another guy, you should always be conscious of the fact that the girl you are flirting with is already with someone else and as such there is a greater likelihood that she won’t welcome your advances.  Further, if it does turn into an altercation, she certainly won’t appreciate you for causing it.  Generally, women like men with honor and they also like men they can trust.  Do you think she’ll see you as honorable if you make your move when she’s with someone else? Do you think she’ll see you as trustworthy if right from the outset you demonstrate your willingness to try to get her to cheat?  Obviously not.

The basic rule of thumb is to not waste your time flirting with girls who are obviously already taken!

So, what happens if you flirt with a girl who isn’t with her boyfriend, only to find out that she has one?  Simple.  Once again, even if she’s being nice, the polite way to approach the situation is to apologize.  Simply tell her that you find her very interesting, but that you won’t bother her now that you know.  You can always ask her to remember you if ever her circumstances change.
The best places to flirt
Some people will tell you the best place to try to flirt with women is at a nightclub or a bar, after all, those are the best places to pick up girls, right? Not necessarily and, in fact, there are also a few good reasons why those aren’t the best places to meet girls.
You see, it is true that some girls go to bars and nightclubs to meet men, but others go simply to have a good time with their friends and to dance. Also, because it is common amongst guys to think of bars and nightclubs as the place to “pick up a chick”, girls who aren’t going there for the same reason will be in a defensive mode.  As a result, the odds of picking up at a bar and nightclub are higher if you’re lucky enough to approach a girl who is there for the same reason, but if not, the odds are also higher that you will be rejected outright before you even have a chance to strike up a conversation – assuming you can over the noise.  Further, nightclubs and bars are filled with other men competing with you for those women who aren’t on the defense, so in the end it all balances out to the point where the odds of rejection are just as high as anywhere else.

Rather than allow this knowledge to lower your spirits about approaching girls at bars, let it raise your confidence about flirting with girls outside of those bars.  The beautiful truth is that often your chances of success will be much higher when you successfully ‘connect’ with a girl in a place where she is less likely to feel defensive.

To avoid flirting at a time when she’s not going to be so defensive, don’t make your move when you’re both mostly alone in a private place, as she may feel concerned about your true intentions.  Don’t make your move on a girl who is clearly in a hurry, or who is preoccupied with something else that will suck her attention away (such as if she’s trying to talk to someone else).  The kinds of places where your flirting efforts will work best are those that are highly public, such as libraries, supermarkets, shops, restaurants and even in the street.

Most guys who flirt tend to do so from a position of stress, concern, and if they find themselves rejected, with anger.  When you talk to a girl she can pick up your ‘vibe’, just as you can pick up the ‘vibe’ of other people.  The last thing you want is for someone to pick up the vibe that you are a serious or stressed out person, or, ultimately, a person who is angry and unlikeable when they don’t get their way.  You can avoid all of that by approaching the whole task of flirting as a fun and playful activity.  Always remember that even the girl that rejects you might be the girl that ultimately takes an interest in you if you respond to her rejection with a smile and a joke.