This is a very important aspect of writing literary fiction especially if the work in question will be focusing on any number of issues: economical, social, political, psychological, and so on. The first thing to do when you've decided to write literary fiction is to, of course, find a theme. Focus on a theme, and find ways to expand on it. Try not to have several deep themes in one book, you might get the reader a bit confused and scrambling to pinpoint what exactly you're trying to show. If need be, try to get your themes interconnected, i.e. not too far off point from one another.
Start your research on the theme you've decided on, and read books concerning it. If you're using real places in your book, you want the circumstances surrounding those places to be factual and true. Your characters are fictional, but to concoct an engrossing theme that reveals something about your characters/the human condition, you have to place your characters in a realistic setting.
For instance, if the setting of your plot is to be during WW1, you must get your facts right about events that actually happened at the time, their dates, year, and so on. If your story is, say, centered on the catastrophic 9-1-1 attack of 2001, you have to do your extensive research and get all the facts right about the events of that fateful day. Do not write what you 'think' must have happened, or what you think you may have heard on the news at the time. If you're writing about the human mind, psyche, and so on, do a proper research on that as well. If your story is to be based on colonial times in Africa, be sure to do extensive study and exploration; read much on the topic, and ask lots of questions. Some issues are sensitive while others are not; but either way, let the facts that you present be concrete and real.
In the book Tell Me Your Dreams by Sidney Sheldon, the underlying issue that Sheldon explores is on Multiple Personality Disorder: how it operates, different situations that might trigger the disorder, and the major effects it can have on others.
In the African fiction Purple Hibiscus by Chimamanda Ngozi Adichie, we see colonialism as the underlying issue that leads to the central theme, and how they all tie back to the main character Kambili and the conflict surrounding her immediate family.
In George Orwell's allegorical fiction Animal Farm, we are shown the fundamental controversy of political corruption, with implicit reference to the period of the 1917 Russian Revolution. We see what Orwell is trying to tell us about war, political patterns, rulers, and how power can change dictators once they take their positions in office.
The books mentioned above involved intensive research long before the books were started. Begin your research now, and make it thorough. Whatever factual events you mention whether in passing or with the purpose of expanding on it, do make sure that it is accurate.
I frown in disapproval when I read books that give incomplete facts about actual events or places; for one book in particular, it was obvious that the author was influenced by the stereotypical depiction of the place in question, and did not actually spend time in a reference library to find out the real facts about the setting he chose to use in his book.
Research is absolutely important for any author of any genre, and a literary fiction writer is not exempted from this rule. Do your research, and do it well!