When it comes to developing a story, the devil really is in the details. You want to pull out all the details that enhance the story. What happened? Describe it. How did the character react? What happened next?
The longer you can keep this going the more developed your story will be. If you get stuck, try changing an event. For example, my first novel was originally a 40-page chapter in a larger book. When broke the book into pieces the chapters had to undergo some major revision and development.
To develop the first chapter I changed the ending. Instead of catching the bad guy, I let him get away so the heroes must chase him. But they had no way to do this so I had to think up a way. All of this adds details and events to the story.
Then I throw roadblocks in their way during the chase to keep the journey interesting. Then they arrive at their destination and proceed cautiously until they find the thief and then more obstacles because the thief doesn't have the item he stole any more.
Later I added new scenes where the heroes are betrayed by one of their own. More details and events. All of these allowed me to turn a 40-page chapter into a 70,000+ word novel.
None of this was easy and added months of work to completing the book but it was worth it. So think about the scenes you are writing. Add the details and action that will help propel your story forward.
And don't forget about character development. You can have a great story and flat characters that will turn off many readers. Get the characters involved. Show how they react. Have them draw on their experience and offer suggestions. Of course, this means you must know your characters well. But that sorta goes without saying.
And above all, keep writing.