Ah!
World-building is quite important for a sci-fi or a fantasy series. Try to visualize how the world looks in your head and then be as descriptive as you can, then work backwards from there to remove what details you feel are too in-depth.
Spend some time on the side building the universe lore and backstory so you have something to refer to keep your story consistent and as a way to work on your worldbuilding. Also, if you haven't already, you may want to specifically define traits, culture, and appearances for each of the core species. Also, get into details about how the various places in the story are supposed to look and keep it in the same place as your lore and race/species traits. Then make sure you have your character profiles defined so you reduce your risk of putting the character out of character.