The Middle of your story is where complications occur and tensions rise for your main characters(s). As they face the road blocks set in place by the antagonist or situation, your character changes as they work to resolve the problems. Your protagonist needs to grow and change as they meet and overcome each challenge they face. Minor situations introduced in the beginning can be resolved in this section of the story. Even though the minor things are settled, you are still writing toward the climax of your book.
In this section of the story, you need to continue holding the reader’s attention, keep them going to the final section of the story. The muddle — sorry — middle of the story is much harder. It is so easy to get bogged down in details, introducing new minor conflicts for your protagonist as you go along. It’s also easy to lose your way in your story and you may find yourself unable to continue. This has happened to me many times and I never enjoy it. If you find yourself stuck, go back and read through what you’ve already written. Make notes of what has happened and what still needs to happen. A trick I used to get past this roadblock was to write part of the ending. This allowed my subconscious to work on the problem and I was still able to continue writing the story.