There are probably millions of blog posts and articles on this subject on the internet. A google search will find them for you, and there are definitely some gems. But I want to focus on a specific part of world building for this post: the details. You don’t want to create the potential for an ocean filled with all its wonder-filled depths, and leave your reader standing in the tide pools.
How real your world feels comes down to the tiniest of details. Does everyone speak the same language? And what language is it*, exactly? What part of the world does this take place in, or is it based on? If you want to evoke a Mediterranean feel, giving towns (and people) American sounding names isn’t going to accomplish the desired effect. Is the world supposed to feel medieval? Then you’re not going to want fancy modern bedding. Are your characters magical? Consider how it works, down to the last detail.
Even if it doesn’t all make it into your ms—which it most likely should not—you should have a grasp of all the inner workings of your world. It will make it more real to you, and that will be clear to your readers. The small details may be small. But they also might be the most interesting. Just like some of the incredibly cool creatures at the bottom of the ocean you’d totally miss if you didn’t leave the tide pools.
*this doesn’t mean you should necessarily try to invent a language. Unless you’re a linguist, you should probably stick to the basics. Just my opinion.