I love writing the beginnings. They are so much fun to write. You divide your book into thirds... the beginning, the middle and the end.
For the beginning, you introduce all of the characters and what they are doing when the story opens. Then something has to happen to tell your readers that problems are coming and then these problems will give your readers the push to want to see what happens next in Act 2 or the Middle of the book.
A Book Structure
Act 1... Beginning
Act 2... Middle
Act 3... End