Basically, you fake it till you make it. It might help to come up with an alternate persona until you start to gain the actual confidence to do it, sorta like training wheels. Not a totally different person, just the person you wish you were, that totally confident and wonderful person you hope everyone sees you as. If there’s a specific boy you have in mind, you can create some talking points beforehand to help you get a conversation started – ie “So, you’re in the Science Club?” “Yeah…” “Cool, what’re you guys working on right now?” “Making a lemon clock” “Really? So how do those things work, anyway?”. Pretty much anything you guys have in common – a class with a really hard teacher you can kinda bash a bit, how crappy it is that the school’s AC is broken, whatever – is a good conversation starter. So is asking him about pretty much anything in his life, save for really personal stuff (so if you know his parents are getting divorced, don’t ask about that). As a general rule of thumb, guys are just as terrified as you are of making the initial contact, and will be relieved that someone else took the initiative.