As an SF writer tending in the space opera direction my shorthand is "make the physics work. Once the physics work, make the biology work accordingly. Once the biology works, make the culture work based on that."
To my way of thinking, there is a certain degree of handwaving you will have to do to make genre work. (In space opera you need to handwave an FTL drive. in UF you have to handwave how magic works, or, if you have a secret world of werewolves and vampires alongside our own, you have to handwave how they fit with the mundane world and how they work internally.) I think the more solid you make the stuff that you are taking from reality, the better that will hold up the stuff that you are making up; so if you're writing about renaissance history, talk to some Renaissance historians and get them to beta. If you're writing something set in Montreal in 1980, talk to people who lived in Montreal in 1980, and so on. (Space opera is much easier than urban fantasy or historical fiction this way. Nobody's going to nitpick you for getting the cultural details of the beings living around Epsilon Aurigae wrong so long as you make them hang together in an internally plausible way.)
The corollary of this is; never write in any detail about guns, horses, or sailing ships. The world is full of people who will always know more than you about those topics, and many of them are on the internet and will say so at length.