Hi,
first avoid to approach her from behind, generally she is not going to like it and it seems like you've followed her. Try to get an eye contact if you do, smile not like this

or this

but in friendly way like this

for 1 or 2 seconds before starting to talk with her, generally she is gonna smile back. Greet her ( a "hi" is enough ),then try something original. I said something to a 8 last week; It was like " hey look at you, I think there is a color missing on your shirt ?!" she wore a shirt fulfilled with different colors, she laughed and we started to talk . I advice you to watch some infield daygame on youtube. Internalize some patterns, try them and you will feel more comfortable when you will arrive at that point, you'll develop your own openers, patterns and routines.
PS: I'm not a expert but I've never been rejected since I've stared pickup in street few weeks ago.
