Why this story? Why now? Why should people care? Why do YOU care?
Whether writing a broad comedy, in which you can finally take a mocking revenge on high school bullies, or a gritty drama that sears the soul with the aching beauty of the human experience (wow, that was over the top!), make sure you distinguish between merely wanting to write and being compelled to write this story, right now.
If you don't feel a thrill of excitement at the idea of typing Fade Out on the story you've got bouncin' around your cranium, you probably don't have the right concept lined up. Because if YOU don't care, why should anyone else?