Setting is the lifeblood of your story-world. You need it to be believable and engaging so that readers can slip into this place you’ve created. In some ways this can be easier when you’re creating a fantasy because you are the only expert on the world you’ve made. If you’re basing your story in a real world location, you have to put in more research. The setting you’re working with should be as familiar to you as your own home, or at least appear that way to the reader.
You don’t have to always include all the details you know about your setting, but it can help authenticate it. If you’re writing in a different time period, be aware of laws and restrictions as they would apply to your characters. What would be considered taboo or strange to them? Adapt those for the modern reader, explain it as needed. If you’re working with a foreign location, learn the customs, the foods, the history, because all of that is going to affect the world around your characters.
Elements in the setting can influence the plot, creating obstacles and challenges for your characters to surpass or be struck down by. Let’s look at something common for hist fic and romance; say for example we’re going to set our story in Victorian-era London and 
our MC is a young woman. What are the laws that restrict women’s movement and prosperity? Is our character married? How does the yes or no of that question affect her mobility in life? Do they have a career? What was available to women at the time in this location? What part of London do they live in and what does it look like? Smell like? Did they have sanitation, public transport, etc. at the time you’re using? All of these factors, and these are only a minute few, can have huge implications on your plot and how your character can move through the world.
Don’t let yourself be lazy with setting. You don’t have to talk about every detail you know about the world you’re using, but you do have to be aware of them and navigate your characters accordingly. 
These are works of fiction, so you can bend the rules a little, but if you disregard them completely people are going to notice and at that point it just looks like lazy writing. Not everyone has the benefit of living (or being able to travel to) where they write about, but the internet is a very helpful tool. Social media connects the globe. Get in contact with people who live where you want to write about, ask them questions, get whatever information you can so that a reader who lives there would mistake the book for having been written by a local.
Writing is all about creating something the reader can immerse themselves in. Crafting a believable setting is an important part of helping readers sink into the story and smoothing the facts and details seamlessly can help keep them there.
Happy writing!
-Erin