This is something I've been dealing with for a while, The only hard thing for me is getting over the little wall called not doing it. I've become decent at that and would like to share some stuff now.
How to approach.
#1 Clear your mind. Do not think about it, Fuck the 3 second rule just do it without even thinking about it.
#2 Angle of approach, NEVER walk directly to a girl it is intimidating and socialy awkward on your part because you will start to think. NEVER approach from the back, it's creepy. Instead approach from the side or straight but make a little curve in your path so it isn't direct.
#3 SMILE. Always smile on the approach, hell when in doubt smile! Don't be the creepy guy who never smiles. Watch some eek the cat or monty python before you go out capture a scene in your head and think about that before you appraoch
When your set hooks smile a bit less but still smile. You want to be the active the fun guy, a smile gets this done.#4 Be clear about what you are saying. You need to let them know what you are saying instantly, If they say ''What?'' in a non understanding manner you failed or didnt do well, and have to ''re-open'' with a second opener or the same one. Make sure they hear your voice and that your body language is concruent with your style.
#5 Watch/listen to the responses to your openen. And use the response to get the conversation going.
Also I would like to add that people are generally polite and if you pay attention to these 5 points you should atleast get a neutral to good response.