Aspiring Authors and more ... discussion

So I am currently writing a book about a suicidal teen who is sent on a mission to find her "friends" which she has never actually met and isn't even sure they exist. Once she finds them she also finds herself trapped in a situation where she has to now fight for the life she'd been trying to get rid of for years (some details subject to change). I often find that when i write I rush along the story and when I try to draw it out I often don't know when to start certain major events. Any advice?