If one is describing a gala ball, what level of detail of the room is considered appropriate? For example, if the ball is a lavish one, is it appropriate to include the table settings (conical red napkins, crystal wine, and water glasses, etc.) or is the designation "lavish ball" sufficient?
Focus on the viewpoint character's attention and opinions.
Describe whatever the viewpoint character pays attention to, especially if the character has an opinion about it.
Don't describe anything that the viewpoint character pays no attention to.
Dale Hartley Emery answered
With this principle Zola's books would be short stories and The Lord of The Ring, a novella. A good portion of the world fiction would be reduced to shreds.
My answer as to the level of detail would be that it depends on your skills. Some authors can write pages after pages of intricate details without boring the reader, other authors make you speed-read and jump any bit of description.
Also, it depends if the description is needed or not. Is the environment an important character, are you writing an atmospherical novel?
Just saying "lavish ball", would be enough only if it is the umpteen unimportant ball the character attends.
If the setting is important yes, I would like to know details about the napkins, glasses…mesmerize us, show us the wonder of the child seeing it for the first time, regale us with minutia, show us that it is lavish…do lavish in the details.
Agreed. But some stories are told by an omnipotent narrator, so more care must be taken to stop describing things before the reader gets bored and skips ahead.
In general, I'd suggest having people read your work and be brutal about critiquing it. I like adding a note where I lose interest in the narrative and feel like jumping to the next paragraph.