Some writers refer to the middle of the screenplay or novel as "the second act swamp." You're past the fun of introducing your characters and getting the story rolling, you've added one or two complications, but you're a far distance from the end.
What to do when you get lost in the swamp? Here are three suggestions:
* Revisit the question of what your protagonist and other characters want. How has this changed since the beginning of the story? It may not be a big change, but even a small one can give you an idea for additional scenes and developments.
* Brainstorm how any minor characters you introduced in the first quarter or third of the story might have a bigger presence in your protagonist's life. Don't be afraid of coincidence as long as you follow the old rule: "Coincidence is an acceptable way to get your character into trouble, but not an acceptable way to get him or her out of trouble."
* Consider whether you need to go back to the first part of the story to plant something that can pay off in the middle.
With some extra thought, you'll get through the swamp!
There are lots of practical writing strategies in my book, "Your Writing Coach," published by Nicholas Brealey Publishing and available from Amazon and other online and offline booksellers.