So ignoring the urge I have to start showering you with compliments on how awesome your posts are, I think I'll leave you with a "WOW YOUR POSTS ARE SUPER AWESOME" and cut right to the problem. There's this boy. Let's call him Dave. Needless to say I've fallen hopelessly in love with him over the course of the past year, and taking from a lot of things he does (gets suddenly flustered around me, looks over at me a TON, is generally very nice, looks over at me some more) I've arrived at the conclusion that he almost certainly likes me. Not to mention that my friends agree with this diagnosis and I've seen some of his friends tease him in that "YOULIKEAGIRRRLLL" way around me.
So that's great, except for the whole problem part.
Dave is literally one of the shyest people I've ever met. He's generally pretty quiet around his friends but he's mildly talkative, then I show up and we're plunged into complete and total awkward silence, save for a few meager attempts at starting a conversation on my part and meager ones to keep it going on his. This wasn't as much of a problem at first since the current infatuation started out as a little crush, and I could end up doing most of the talking while getting a little fluttery and it worked. Now, however, this little crush has evolved into something that turns a really bold, loud, outgoing girl like me into someone who can't formulate a complete thought, let alone say one. I've tried going into conversations with him with some possible conversation topics floating around in my mind, but it always happens that my mind goes completely haywire. What would be witty banter between two other flirting teenagers is something more along the lines of mumbling stupid and incomplete sentences on both of our parts. Regardless of whether or not this is normal for him, it's not normal by any means for me.
So the question is pretty much this: I really really really like Dave and I'm 99.999% sure he likes me, but we can't actually manage to talk to each other. What should I do to keep conversations going between us, and (more importantly) actually flirt with this boy so he actually knows I'm flirting with him but isn't immediately scared off?
This is normally where I'd offer some anecdote about myself in high school, e.g. "I once tried to talk to my crush, but all I did was say 'Excuse me,' and then fall down the stairs," but I don't even have to go back that far. This still happens to me. What should make you feel a lot better about yourself is that this also still happens to everyone. I know a girl who's much more composed than I am, and I recently saw her respond to a compliment by saying "Thanks, I warely rare this," then correcting herself with "I... warely rare this," and then just sort of hanging her head in defeat. So I don't think this is one of those "help me Jono, my brain has brain problems" questions; I think it's something anybody might experience when really attracted to someone else.
You asked how to flirt so he can tell you're flirting but he isn't scared off, and my answer to that is usually some variation of "start slow, talk to him a lot, and gradually say increasingly flirty things until he gets the picture." But since both of you are still stuck at step zero here ("Form a complete sentence"), I'm just going to concentrate on the talking part. Here are some ways to have a coherent conversation with a dude even when your brain is constantly trying to ruin everything.
Prepare in advance, but not too much.
I don't want you to actually write down a list of sentences to say out of your mouth next time you see him. This will just lead to you going "GREETINGS EARTH HUMAN, HERE ARE SEVEN QUERIES FOR YOU, BEEP BOOP." Nothing makes conversation sound more wooden and artificial than when you've literally memorized it. But if being around this guy makes you blank out completely, then it will help to have an idea of what you're going to say in advance, so you're not just standing there wordlessly opening and closing your mouth like a goldfish. You said you've already tried having some topics floating around in your head, which evidently didn't work, so be more rigorous about it next time; have a couple of specific conversation-starters to ask him about. Don't stress over this too much, and super don't force your conversation-starter in there if a separate conversation has already started. The entire point of this step is to have a couple of specific prompts to get him saying actual sentences. If that already starts happening organically, skip to the next section.
Ask followup questions.
People like talking about themselves; they feel flattered when people take an interest in them, and they don't have to work too hard on their answers. So once you ask him something that gets him answering you, ask a followup related to something he just said. For example, if you ask him what he did over the summer, and he's like "Oh, not much, spent a week at my parents' beach house," don't be like "Oh. ... ... QUESTION TWO, DO YOU LIKE CATS." Prod for more information; ask him where it was, what it was like, whatever. Get him talking about his own experiences. I've mentioned before how effective it is to be seriously, genuinely curious about the guy, instead of standing there with cartoon hearts floating over your dumb head the whole time.
The only danger with this method is being too interrogative; you should be sharing stuff about yourself occasionally, too. If you're asking questions so relentlessly that he's getting visibly flustered, or if you're asking questions like "Where did you hide the body??" then you are being too interrogative.
Just work through the awkwardness.
The awkwardness fades with time—and I don't just mean over many conversations, I mean within a single conversation. Eventually your brain settles down and remembers what a sentence is again. Initially, your brain is bouncing off the walls, going "OMG HE IS PRETTY," but after a few minutes, he will still (presumably) be pretty, and your brain will calm down, straighten its tie, and go back to functioning as normal. Or at least, this was true for me, and I was basically the worst of dudes, so I'm confident it'll be true for you.
Really, all of this just boils down to different ways to calm yourself down—it's calming to know what you intend to say instead of thinking on your feet, it's calming to concentrate on the other person instead of yourself, and it's calming to stand there talking for sixty seconds without any embarrassing disasters happening. Once you've gone on for long enough without any of your sentences coming out like spaghetti, your brain will be like "Ohhh, I remember now," and you'll find yourself able to talk to this guy just as well as anyone else.