Samuel R. Delaney has talked about the importance of reading protocols, and reading SF as SF. I tend to read everything as SF. ...What Walton means by saying she reads everything as SF is that she is always aware of contextual clues that give her hints as to what the world in the book is like.
People talk about SF as a literature of ideas, as if you can't find ideas in Middlemarch or The Hunt for Red October. I don't think it's so much the literature of ideas as the literature of worldbuilding.
In a science fiction novel, the world is a character, and often the most important character.
In a mainstream novel, the world is implicitly our world, and the characters are the world.
In a mainstream novel trying to be SF, this gets peculiar and can make the reading experience uneven.
Jo Walton, What Makes This Book So Great
I, too, read everything as SF in that same way. Which makes Dickens and Eliot and all sorts of other authors much easier to dive into, let me tell you.
And Walton puts her finger on why I have never really cottoned to mainstream authors' "science fiction" books. I'm expecting science fiction and they're just donning the costume in order to deliver a different sort of book altogether.