Before you start to write your book, you should summarise the plot of the story in one sentence. This helps with not forgetting the most important events in spite of many creative ideas. But the sentence should not only be a summary of the story, it should also contain the main conflict. In each book, you can find a lot of conflicts, but the main conflict is like a red line leading the reader through the story. The summarising sentence should be as simple as possible. If the sentence is too complicated, then maybe the story is too.