My advice: When describing something, ask yourself what is the most striking thing about that thing.
For example, you want to describe a city. You may ask yourself: are poor neighborhoods very visible? Are the people well dressed? Distrustful of travelers perhaps?
That way, you stay focused on the most important points, allowing yourself not to drift off and tell irrelevant stuff that nobody cares about. Of course, some people love to write long descriptions for anything and everything (like me), whether it's important or not. But you do as you want.
That was what to describe.
Now we can tackle the vocabulary. When you describe something you can sometimes feel that it is missing something: that it is not impactful or in-depth enough. When this happens, try to change your sentences, to modify them slightly to make you use more vocabulary; rarely used synonyms that can sometimes have more meaning than a whole sentence.
It is also important to remember that a description can be too long. In combat, the goal is to feel the intensity and impact of the blows (most of the time), so some will use short but direct sentences to support actions. But if in a supposedly heated fight the author suddenly writes a three-paragraph description, the readers will not understand. It would break the rhythm of the scene.
I don't think that's all, but nothing comes to my mind at the moment so I'll end there.
I sincerely hope this has helped you.