I HAVE NO IDEA HOW TO FLIRT?

I flirt for fun sometimes, but I really can't do it if I'm really interested in someone.
So, tonight I'm going to a pub and then clubbing with my friends and my crush.
I really wanna flirt with him, but don't know how!! I'm really shy so it's not easy for me. I can do it if I'm not interested cause I know I have nothing to lose and I can be more direct.
But I kinda really like him so I don't want to look desperate but I'm afraid that if I'll be too subtle he won't notice it.
Any tips? Girls, how do you flirt? Guys, what do you like? How to understand if he's interested? He used to like me but now I don't know how he feels. One of his friend told me that if he knew I'm into him he'd text me in a heartbeat but I don't know.
I HAVE NO IDEA HOW TO FLIRT?
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