Help! why am i so shy around him?

There's this boy i like, and every time he looks at me i look away quickly and blush. I want to subtly let him know that I'm interested, but i'm way too shy to randomly talk to him. All my friends tell me that i have the capability to be pretty and flirty, so i always wonder why he doesn't notice me that much. How can i discreetly let him know i like him?