Ouch! How did that desk get there?
Let's say your wealthy and titled hero is sitting in his office. Hmm. There ought to be a desk and a chair for him to sit on. What else? Windows? Rugs? Paintings? Fireplace? Other chairs? Any tables? What color are the walls? If you've done your research, including reading about architecture and furniture, you know the answer to a lot of those questions. You can pick some authentic item and have the hero or heroine, who's going to come in any minute now, use it.
OK. There are three chairs, you've decided. When the heroine comes in, which one does she sit on? The choice might be instructive. If you don't have these details in mind when you're writing, you'll probably never think of using the choice. She'll just come in and sit when invited. Your reader will not be thinking, hmm, how interesting that he asked her to sit there...
How come nobody bumped into a desk yet?
What if you haven't really thought about what's in the room? You just say the hero is sitting in his office because that's a manly thing for him to do. The heroine comes in. They converse, things get heated and they passionately embrace. Hey! says the reader, who is not stupid, and is therefore thinking office, desk, chair. How come no one bumped into the desk? Or worse, he has the absurd picture of your couple reaching for each other over the expanse of the desk, their lips barely able to touch.
This isn't hard at all. Find a passage in your WIP with people in it. Imagine details about the things around them and then use a couple of them. Send me a quarter if, when you finish, your scene has drastically changed.
Do that everywhere. Imagine all your rooms and spaces and use some details.