approach invites are not needed, but if you want to improve the amount of approach invites i suggest the following first check out this thread and read the part about approach invites, so you can tell when your getting one
patterns-i-have-noticed-vt96463.html
next, if you want to improve the amount of them you get try the following,
1)get into state (happy mood)
2)pick something to think of that will sub-communicate an attractive confident quality
(for example, I AM SO FUCKING CHARMING, NO GIRL COULD RESIST *can be anything that will positively effect your sub-communications*) just repeat this over and over in your head until you are truly believing in it
3)slow your movements down, relax, walk slower, try to actually feel powerful as you move, like all your movements are very powerful and you are important,
4)do not check out girls, just focus on what you are focusing on, do not react to anything, if a girl passes your vision, do not flintch of look away everything that holds your attention does so because you choose so, you are not reactive, you do not look away or at anything too quickly unless it garners your attention and rightfully deserves it
5)dress in an attractive manner, dress in a manner that would be attractive to those that you would like to attract, also all out pea-cocking (the more you stand out) the more attention you will receive (forced looks, not necessarily attraction just attention)
6)do your hair nice don't keep it plain, get a haircut and style it, just groom yourself in general
NOW DO NOT DIRECTLY STARE, JUST CHECK YOUR PERIPHERALS FOR GIRLS LOOKING IN YOUR DIRECTION, WHEN YOU NOTICE IT, SLOWLY TURN YOUR HEAD LEADING WITH YOUR EYES TOWARDS THE GIRL LOOKING IN YOUR DIRECTION, LOOK FOR THE INVITE, THE MORE YOU ARE ACTUALLY PAYING ATTENTION AND CONSCIOUSLY TRYING TO NOTICE THE INVITES THE MORE YOU WILL SEE THEM,
just think though of when you are walking and another guy who is bigger and more intimidating then you snaps his head at you and stares at you quick, the natural reaction is to look away fast, same for girls but they are even more timid and less confident (usually)
anyways i hope this helps you