When you are describing a character it is important to remember that you're not just describing what they look like, you are giving a piece of their history. The clothes a character wears is more important than just fabric used to cover their body. It can be used to indicate their social status. The color of their shirt can tell you what groups they belong to. Little details like that serve two purposes: (1) they flush out the character and aids you in world building and (2) it can give you an opportunity to go into their history and backstory.
Ex: In 'Penric's Demon' the author first describes the main character by talking about his outfit. He notes that his clothes are all hand-me-downs and that the character had to hem it himself as well as make his own repairs. This became a jumping off point to describe how the character is the seventh child and third born son of noble house that had fallen on hard times.
This same advice can be applied to describing a place. Every bit of detail that can be added to a town, building, ship, castle, home, or whatever can be used to describe their history, significance, and connection to the characters.
In the case of writing a description of a place where a scene is about to happen, spend a little time beforehand to give a layout of the space.
- Where is the door?
- Where does the light come from?
- What kind of furniture is there and where is it placed?
- Where is everyone standing?
All this prepares the reader for what is going to happen in the scene. It primes them with all the knowledge they need so that when the scene happens, there isn't some element that just pops out of nowhere. Therefore when you write this all down be sure to only include the essential details, things that are going to be used during this scene or some follow up one. Don't describe a chair if no one is going to sit in it or use it to club someone.
Tl;dr: Describing a character or place should be an opportunity to give the reader their history and what makes them significant. When writing a scene, take the time to block out all the important elements first.
My esoteric advice: Watch videos of people who make cosplay costumes and listen to them describe every detail of the outfit they're making and how it fits into the story of the character.