How much is too much detail? It all depends on what you are writing and its genre.
Here’s a handy rule of thumb...
Short fiction is a single snapshot of life set in words. Leave the promo video in words for a novella; the two-hour blockbuster movie, complete with sound and atmospheric lighting, for the novel.
However, this doesn’t take into account the genre. A pithy, kick-ass thriller with a high percentage of dialogue and a non-too realistic take on violence will drown under detail. A ghost story will come across as limp if atmospheric detail is removed. Where would an epic fantasy be without the detailed world-building, or the claustrophobia and mind-numbing routine of interstellar space flight?
Getting a handle on how much is too much comes with practice. The big no-no is the info-dump – a page or half a page of description that no character plays a part in. And that includes characters standing in front of mirrors describing themselves. That’s pure authorspeak. Give the reader a break here! A novel is not about its author.
Reading widely within your genre develops mental boundaries, not just for the genre, but your own reaction to it as a reader. It also comes from trials.
Come up with a simple scenario: your focus character leaves his/her home base to gather supplies. The character is in a calm frame of mind; on the way the character meets someone who isn’t.
Now write that as a kick-ass thriller, a ghost story, an epic fantasy, an SF, a romance, a Western, a....