I know the entire story. I'm just not sure how much to tell.
Answer:
Tell only the parts that show more about:
1) the character emotional development -- this info should come in stages, revealing deeper and deeper layers, the deeper and deeper the reader reads
2) the theme -- as the plot advances, the thematic significance of the story deepens
3) the dramatic action -- action becomes dramatic when filled with conflict, tension, suspense, and / or curiosity -- the sense of threat is both internally and externally driven
4) the details that make up with world the characters live in -- use only authentic and specific details and go for as much symbolism as possible
Tell nothing more. Show nothing less.