What to do?

I know I am not the best writer, and I didn't take any college courses in writing or journalism. My ultimate goal is to write a book. After reading The Twilight Saga, it gave me a passion to read more about stories like that. I know of a few that is out there, but none have caught my attention. I wanted to write my own, but I am lost! Coming up with characters, the plot, the story line is mind puzzling! It is a dream of mine, that I hope to do some day. I am hoping that blogging will help strengthen my imagination. How is it, that I want to write a book but I have nothing to write about! I don't get it, but I look forward to doing it, and any thoughts that anyone has feel free to give me a shout!