Make us believe there's a world beyond your characters' surroundings. Even though you can't spend tons of time on world-building, you have to include enough little touches to make us believe there's stuff we're not seeing. It's like the difference between the fake house-fronts in a cowboy movie and actual houses. We should glimpse little bits of your universe, that don't necessarily relate to your characters' obsessions.
Fuck your characters up. A little. Just like with worldbuilding, you can't necessarily devote pages to your characters' childhoods and what kind of underwear they wear under their boiler suits. Unless your story is really a character study with a bit of a science fiction plot. I used to have a worksheet that included spaces to fill in in info about each character's favorite music, hatiest color, etc. etc. Never filled those out. If I'd tried to force myself to come up with a favorite color for every character, I would have given up writing. But do try to spend a bit of time giving all of your characters some baggage, just enough to make them interesting. Most science fiction readers are interested in characters who solve problems and think positively, but that doesn't mean they can't have some damage.