Critics insist that art imitates life in order to achieve meaning. How do you make a fictional world look real? There are a few aspects that are especially important.
In many cases, fiction is not particularly realistic if you look at the "big picture," especially in the case of speculative fiction or an unreliable narrator, but the reader is drawn into the world and propelled along by the details. You don't have to crowd your story with thick descriptive passages in order for it to seem real. A few details in the proper places will make all the difference. If you have had this experience while reading, you already know what it takes. (If not, look for it the next time you pick up a book!) Sometimes it takes several revisions to find out what works and what doesn't in this department, and what is important and useful to the story. Many times detail has a particular thematic relevance. In any case, every detail should fit with the piece and work hard.
You probably know already that dialogue does not have to, and should not, imitate real-life ways of speaking exactly in order to create the appearance of reality. However, characters risk coming off as not particularly believable if dialogue fails to show their various motivations and nonverbal modes. Try to delve into the realities experienced by each character in order to avoid contrived dialogue. What is each character trying to accomplish? If their motivations are true to life, the dialogue will be realistic. Punctuating dialogue with gesture also helps, not least because it affects the pacing of dialogue.
Avoid cliche here. It helps to think like an actor, and eschew the obvious stock gesture in favor of gaining an understanding of what one individual would do in one particular moment in a story. If gesture is too unorthodox or too typical, it risks calling way too much attention to itself. The most important thing is that it is characteristic and appropriate to the situation.
Knowing You Audience
When you read stories that seem dated, or by someone who is clearly from a different walk of life than you, their world will often seem a bit strange and incredible. Classic literature often includes minute descriptions of social customs that are entirely unfamiliar, which a reader has to navigate by instinct. As long as characters are believable and the story has its own internal logic, this is possible, but if you know who you are writing for, use that to your advantage. What are the themes, manners, and details of their world that they will recognize in fiction?
Creating verisimilitude in fiction can be counterintuitive, because it often has nothing to do with trying to recreate the entire objective world in print. Execution is everything. It's a bit like theatre, where you must use limited resources and knowledge in order to create the semblance of a much larger world. It's often the focus on "the little picture" that allows this to be done effectively.
Francine Prose, "Reading Like a Writer"http://en.wikipedia.org/wiki/Verisimilitudehttp://www.reflectionsedge.com/archives/dec2005/vatcc_hb.html