Seriously, I need A Playbook at this point...(Girls Thoughts Would be Great)?

Alright so I've been going through this crush on this girl at my school, for a long long times, really its quite pathetic at this point, I cant seem to go after her for some reason. Always what happens is that she's "talking" to someone else so I get discouraged to even try or shes simply takin. The most common reason is that I have this thought in my head, that she doesn't like me like that. I really dont know this but I think a lack of confidence plays a part and really I'm not a shy or unconfident kid, its just when it comes to her I, freeze, believe me I try to make conversation, but I really just cant seem to keep a good one going, she also seems shy around me to. Its really just a weird and unnecessarily complicated situation. At this point I'm really done with this though, I want to be with her soo bad, to a point where I feel like I will never get over this crush, trust me I've tried (haha). But what can I do, I dont want to come off as weird or desperate, because we havent talked since school, but I need to do this! Anyway enough with my vent, I really would just like to get opinions on what to do and how to go about that, yes I know I need to go after her, but how should I go about that? I need help! So tell me what your "playbook" might be if you were in my situation Were soon to be juniors in high school if that matters at all. Thank You!