How do I talk to boys without immediately thinking about desperately I want a boyfriend?

I'm 17 and I've never had a boyfriend! I only have about 2 guy friends. one i'm pretty sure is gay and the other one a lot of my friends think is gay. whenever a guy flirts with me i go along with it but i can't go beyond just being polite. i've been told i'm pretty and i get some glances sometimes but i could never initiate any kind of flirtation! and once i like someone i have no idea what to do and how to get to know them better without making it obvious i like them, which would mortify me! so many times i want to get to know a guy more but i just end up avoiding them. What should be my frame of mind when talking with guys?