One problem I keep coming up against in my own work and other people's is when the theme is too much in the foreground.
Lisa has a script idea about a girl struggling with some issues about her family. But when she tried to make a script about her trying to resolve her issues with her family, there wasn't enough story, and the story wasn't interesting enough.
What I thought she needed to do was make a story about the girl trying to do something in her life, and her family issues become an obstacle -- a submerged one at first, that doesn't come into the foreground until the climax. That seemed to make a better, stronger story. It gave us something positive to root for (stakes), and it complicated what had been too bald and unassuming a narrative.
Likewise, I had a series idea about a character on a quest some identity issues -- she's more than human. But I couldn't figure out how to make stories out of that quest. What I realized I had to do was give her something
else she needed to do, that was at odds with her quest. Paradoxically, by making it harder for her to complete her quest, I made it easier to tell stories about her.
If you think you have a good idea, but the stories aren't coming, maybe you need to move the idea to the background. Make it the secret. The ghost that haunts your character. Make it the obstacle to something your character is trying to do. Often your good idea wants to be in the background for most of the story, not the foreground.