People are lazy by nature, and will pick the low hanging fruit. The girls that act... as you put it... slutty or, flirty... are low hanging fruit. This is to not say that someone will not see the value in you unless you act like that, but remember that patient and thoughtful people who will look further then the batting eyes and bouncing push up bras are the exception not the norm.
Not overly sexual, but flirty yes. Men love it when they don't need to read these stupid signs you women give off. When they flirt, it's obvious she's into you. So girls who flirt generally get more male attention.
Well not really my girlfriend and I werent like that we were best friends and one day we decided lets give this a try and see what happens and yeah it is great better than fake crap that people do to attract each other
No. But flirting helps. You don't have to flirt sexually or anything, just teasing (harmlessly making fun of him) and complimenting him can get you far. It's good to make your interest known because otherwise, a lot of guys will just assume you're not interested in anything besides friendship.