Try creating an outline, and then using that as a reference to
write the story. One of the first books I wrote as a teenager, I
actually did this. I just wrote down an outline first; pencil on
paper. Not chapter by chapter, but event by event. When a major
event came to mind, I would use the top-level outline numbering
and indent level, and then drill down into what would transpire.
It was a great exercise to help train my mind how to write
books. As I wrote the story, perhaps a year later, I remember
finding it easier to write about one event at a time. It was
more like writing a series of short stories. Of course, I
changed things at whim. Through several rounds of rewrites, the
book did eventually come together. I hate to say it, but if
you're writing a story, don't be afraid to just outright use a
formula. I don't do this any more, but have certainly used it as
a mechanism to help get ideas out when I was younger. Just think
about how you think the basic story should flow, and then fill
in the blanks with