^ What Kaylin said. Definitely. Also, setting could mean anything from the city where your MC lives, to where they go for coffee, to what's on their nightstand. Broader settings set the stage for your character, but specifics may reveal something about them. I'll use a character from my novel: She lives in San Francisco. She buys coffee at a hip joint downtown, because the coffee's good and sometimes she sees her ex-husband there. There's a gun and a badge on her nightstand. Bad example, but whatever. The point is, execution is key. Travelogues can be a turn off to the reader, so I suggest only writing in elements of the setting if, again, that pertains to the plot or character. I don't want to know about the cute little apartment on Jackson street if it doesn't have anything to do with either.
I'd be more inclined to use the word believable rather than real but I know what you mean. I'd say what adds a lot to the believability of your world is how your characters interact within it. If they explain everything they do, do uneccesary things, or seem to take notice of everything that's different from our own world all to inform the reader then it will start feeling like a stage. Imagine if you went to a country that you've never been to with a culture you are unfamiliar with. Now your task is to learn about them and their land. Sure you'll get some explanations here and there from the natives but most of that learning is going to be from observation because those natives are going to be so use to their world that they won't notice everything that they are doing.
I find a world comes to life when its inhabitants have different thoughts. For example, instead of making a particularly race all agree on war, some might agree, while others might say no.
For me, the best way for me to make up a setting is to go and actually write out what I want this world to look and feel like. Who inhabits it, what is it's backstory, etc. Then I use that as a reference when writing out my story. That way I can go into a ton of detail to help me write the actual story, without weighing the reader down with a bunch of details they probably could care less about.
I find the best way to make the world come alive is a healthy dose of descriptive writing combined with believable character interactions. Small moments of drama, and seemingly trivial, tender moments create the illusion that the characters inhabit a well lived in place. The way the characters, no matter how insignificant, hold themselves; the way they walk upon the earth and interact with it. The dance of shadow and light across your characters, cast by objects within your world. The way children play with their environment. Just gentle moments of introspection like that punctuating your text will help to make it convincing. A world without characters inhabiting it realistically, no matter how beautifully described, is little more than a static image. Take a little extra time to add those small but significant details.
I'd say that the best way to get people to believe in your world is to leave stuff out. Know more in your head than you show on your paper. That by itself automatically makes your story more in-depth, because readers can tell when you're prepared or when you're just making stuff up to make the plot work. Also, there's implied plot. Basically where you imply that your world is deeper than you portray. Like, if you're writing a scene in a sci-fi school, you have your character read a list of classes to enroll in, and it says things like "Tachyon Particle Manipulation 101", "Beginning Deflector Shields", or "Hostile Species Negotiation I". You don't actually have to write out what any of these actually are, but they imply that your sci-fi school (or whatever) is bigger than you show.
The best way to create a realistic environment i have found is to go outside and write down everything you see. Go to a city and note down everything you see. Go to a farm, note down everything you see. Sight, Smell, Touch, Taste and what you Hear. Do it for as many locations as you want in your novel. Now you have that, all you need to do is modify the location to fit your story, you should have everything the situation needs to be realistic written down. So all you need to do is change the Green grass, to purple grass(if your on another world for example). You could change the sounds of birds singing in the trees to the sounds of machinery in the distance(industrial revolution), or perhaps change the bustling subway to a desolate decaying underground tunnel(post-apocalyptic). You should have sufficient detail to pick and choose what elements you want in your story but you'll have a framework for everything you could need to make the situation realistic. The situation you choose should be reasonably easy for an average person to relate to, your just changing their vision into your story. For example, a subway. Everyone known the subway is somewhat a tunnel, its got lights everywhere, there's stairs, bins perhaps, there's railway signs etc.. All you need to do is state that its desolate, moss filled, thick with the musty stench of fungus growing in the trickles of water that carved crevices into the decaying subway walls. Instantly your in an abandoned subway(obviously you'd do a better job of it).
Engage the reader through is sensors - sight, smell, taste, sounds, etc. Show vs Tell in optima forma....
Research research research. Can't get enough of it. Writing some military fantasy? research old tactics, weapons, armor, and historical battles. Writing sci-fi? Research all fields of science.
Well something that my creative writing teacher always stressed was "show don't tell". People want to visualize things not be told exactly everything that is happening. Another thing I read in a book (forget which one exactly I think it was Stephen King's "On Writing") was that you don't want to over describe the scene. You want to give them specific details unique to your setting and let them fill in the rest with personal experience.
I write fantasy sometimes. I make a backstory, a history and cultures. I draw a map and add geography, try to make the world as full and believable as possible to me. Then, I begin writing from there, slowly introducing my world into the story. Little differences that lets the reader know that this world is not earth. I think it's a little overwhelming to just flood the reader with all these differences in a fantasy realm and some books that I have tried reading that do that, I often stop reading because it was just too much information and I couldn't tell what was important to the plot and what was just window dressing. I hate being confused when I read, it's very frustrating. There is a book that I once read that might help you. It was by Orson Scott Card and it was titled something like, The Writer's Guide to Science Fiction and Fantasy. It talks about world developement and all sorts of other useful things. You could also read fantasies, it might help to see how other authors have done it.
