The basic problems in science fiction revolve around the need to explain yourself to the reader. It is a trust issue. Science fiction readers want a certain level of grounding in their stories, otherwise they’d be fantasy readers. Even then, there has to be an internal consistency to the rules of the magic you are using, especially the rules you make up yourself.
Below are two areas that require the most attention when writing science fiction.
This planet is perfectly suited to our needs. Try rereading that sentence, taking notice of how self-centered and foolish it is. Our needs arose because we developed on this planet and evolved to fit its conditions. Recreating similar conditions on another planet or finding one that is identical to Earth is unlikely at best. Even a 5% difference in the air’s oxygen content would dramatically change how (or if) we live our lives. Different conditions yield different results.
Stories that take place between star systems require faster-than-light (FTL) travel. Unless you want to abandon any sort of scientific authority, starships can’t accelerate beyond that limit. It would take infinite energy just to match that speed and you’d be permanently frozen in (our perception of) time if you reached it.
How do your characters get around this problem? Different franchises use different methods. Star Trek uses warp speed to fold distances in space. Star Wars uses a hyperdrive, as do the ships in the Saga of the Seven Suns. Babylon5 and others, use wormholes. The point is that each one has an explanation of how this is done, rooted in some fact or theory.
An author doesn’t have to go too crazy over these ideas, but simple awareness will help maintain credibility.