Write what readers want to read, not what you want to write (if you want people to read your writing). Ask yourself this question constantly as you write: "Would my readers prefer to learn about the history of the planet Xtron in detail, or would they like to read about a fight, sex, a chase, that incredible new spaceship Tony just built in his garage etc. This is an extremely common problem in all genres. Many fantasy book authors, for example, seem to need to begin their stories by telling readers how the gods created their worlds, and how they like to meddle in the affairs of its population. If the history of your world is important, tell your readers about it, but not all at once. Parse the knowledge sparingly to help build tension.
Here's an example:
"Curse this rocket!" shouted Tony as he tried ineffectually to get his spaceship off the ground.
"Looks like Orangulus, god of flight, is up to his old tricks again", said Cornelius.
"Or maybe I'm just a shitty mechanic."
This exchange accomplishes these things:
- It tells readers that the culture they are reading about is polytheistic and that humans(?) fly through space. Or try to, at least.
- Readers now understand that Cornelius believes the gods meddle in the affairs of humans(?) while Tony is skeptical.
- It adds to the reader's understanding of three characters and begins to develop their unique voices.
- It adds to the realism of the world. Rockets don't always work and need tune-ups (think Star Wars).
Get to action or drama quickly. Build conflict. Readers care about your story (you hope), and want to hear about the world you've lovingly built, but not all at once. Make your readers curious about your world -don't assume they already are.