How to keep a conversation on it's flow?

Well I'm pretty sure there's a lot of question's just like these.. but I myself is having the trouble of talking to this girl I really like I mean we already are talking about every time I fail to bring up a good conversation we've pretty much gone through everything you can think of from Music, RL problems, food, etc. It never usually lasts long and well she usually gives short answers when I ask her questions like "haha lol" idk :/ Advice anyone? Plus I really want to ask her to Prom next school year