Confidence is a key ingredient in appearing attractive to a boy.
Before you approach the a boy, zero in on the things that you most like about yourself. It might be your eyes, your ability to make friends, your sense of humor or your wit and intelligence. Whatever it is, pump yourself up by acknowledging your positive attributes and writing them down or repeating them to yourself. Just don't be overconfident and arrogant when you talk to the boy.
What He Likes
Get a sense of what he likes, and what might align with you and your personality.
If he loves a girl with a sense of humor and you know how to make people laugh, have a couple of funny jokes or stories handy when you see him. He'll remember that you make him laugh and he'll be attracted to that. If you know that he loves a girl with nice legs and you feel confident about your legs, wear a cute skirt that shows them off. Show off whatever qualities he likes in a girl that fit in with your personality, and he'll be interested.
Boys don't usually pick up subtle signals from girls.
If you like a boy, try not to be too mysterious. Find a balance between subtlety and coming on too strong. When you're chatting with a boy, keep it casual and warm. Touching him lightly on the arm or playfully touching his shoulder is a way to show him that you're interested without being too overt. These small physical interactions will also spark his interest.
Stay True to Yourself
Don't try to pretend to be someone you're not when you're around a boy.
Instead, find common ground with him. Ask him questions about himself and what he enjoys doing, and talk about the things that both of you share and the activities you both like doing. Act comfortable around him and make him feel comfortable around you. If you're both interacting genuinely, your natural chemistry will emerge.