I've heard the word "overwritten" quite a few times but had always had a hard time putting a solid meaning on it. I figured it meant that the author was trying too hard. However, some time ago I came across this article, in which Alexander McCall Smith specifically says that overwriting involves too many words on the page (adjectives especially). A quote:
"Something is overwritten when there is just too much of it. This may be
because the writer has laboured the point and made a mountain out of a
molehill, or because too many words are used. As a result, descriptions
are cluttered and the prose quickly becomes unreadable."
Here is the article, if you'd like to see more.
He goes on to say that English is so rich with possible synonyms that people want to use more than one, like overindulging in candy. I know I've done this before - it tends to come out in that place where we get to the end of a description, add a comma, and then add another description. Example off the top of my head.
His eyes were like the night sky, like the horrible depths of his soul.
Now, I have often gone back through descriptions and said to myself, "no double descriptions - cut one of those two out and leave the better one." However, when you take it back to the level of story function, I can think of contexts where two descriptions might work. Those might be spots where you're trying to show a character's ambivalence. The above example might be someone considering a man and thinking about how beautiful he is yet how evil. Sure it can be done differently. Better. More concisely. But I don't think a descriptive echo is always the wrong answer.
I have a tendency to be quite specific in description - but not all description. Only particular types. I look out for places where a reader's assumptions about the real world are about to lead them to wrong conclusions, and that's where I put the words. To close a hole in the story where someone might "fall out." Working in worlds that are not like ours means not being able to rely on as much previous reader knowledge. That means that sometimes more description is necessary.
I also want to look at his phrase "mountain out of a molehill." While I don't know precisely what he intended, the phrase evokes something quite specific for me in the writing context - something I'll call "straining to create intensity." There are points in a story when we want something big to happen. "The big reveal" is what they sometimes call it. "The big set piece." I think you know what I'm saying. What can sometimes happen is that we get to that point, find that it's not hitting with the appropriate BANG!, and try to amplify its effect by getting more flamboyant and intense in the way we write it. Sometimes that can be helpful, but sometimes it just makes us seem like we're yelling and waving our arms on an empty stage. For events to have impact, they need to be supported by the rest of the story.
This is a particular risk when you're trying to follow the adage, "start with conflict." In a movie, where the visuals are so important, you can afford to start with someone in the middle of a fight, or a car chase, or something, because it's just so cool to watch that you can handle waiting to figure out what it means and who's involved. But a lot of the significance of a written scene lies in its significance to the characters, and unless you know the characters, it's hard to feel that kind of sympathy. At the beginning of a story, we want conflict of the kind that effectively evokes personal qualities of the characters, so that we can get to know them. Too much pyrotechnics for someone we don't know can easily result in someone saying, "I don't care" and putting the book down.
A moment of true impact can be a single sentence, even a single word, if it's properly supported. It needs to be supported by our knowledge of the characters and their situation (story-internal information) as well as our knowledge of what kinds of experiences can be traumatic for individuals in our own world.
I wouldn't suggest that you be afraid to use adjectives, or adverbs, or any other part of speech. It's not that simple. It's enough (to my mind) to realize that these things can be easily overused, and to make sure you're conveying your meaning most effectively. Remember, you don't need to put five different descriptions on something - you should put one (maybe a complex one) which best fits with the characters, the world, and your intended emotional effect. Remember also that other parts of your story, like the character personalities, progress of events, or even repetitions of particular types of imagery, can provide a strong foundation and magnify the impact of what you describe.
It's something to think about.