Next week, the twelfth book of Robert Jordan's Wheel of Time series will be coming out, which makes this a great time to talk about description in your writing. I know our audience leans more towards romance rather than fantasy, so let me explain how I got on this topic. Robert Jordan, like many fantasy authors from J.R.R. Tolkien to Christopher Paolini, uses a lot of description in his books. He can go on describing something as simple as a dirt road for pages and pages on end, giving the reader every microscopic, inane, and irrelevant detail on any person, place, or thing. Robert Jordan has many fans. I am not one of them.
Deciding what level of detail to go into in your writing is partly a personal stylistic choice, but it is also influenced by your audience and your genre. For example, in romance your reader expects to know exactly what your leading man looks like--and it better be hunky!--while other details, like what your characters eat for breakfast or what their couch looks like (unless that couch is the scene of a little action) aren't as important. In writing mysteries, you better make sure your reader gets enough information about the suspects and various pieces of evidence that they can follow along as your protagonist solves the case.
In general, the level of description you give a particular person, place, or thing should somewhat correspond to its relative importance in the story. The reader should have a good idea what your major characters look like, the locations where most of the action takes place, and various objects that are important to the story. But we don't need a lot of information on very minor characters or things that just are not relevant to the story. Before you start writing a page of description, consider whether your reader really needs to know that much about whatever you're describing, and when you're editing, make sure you've given the reader enough detail about anything that plays a large role in the story.
And remember, when you're trying to describe something to the reader, show instead of tell.
Besides nouns, there is one other thing that you need to describe: dialogue. Some of you may have heard the phrase "said is dead," and there is something to that--just having a dialogue described by "he said" "she said" is going to get boring. Spice it by using other verbs ("shouted," "moaned," etc.) in the place of said, describing things like vocal intonation ("her voice squeaked as she started to panic"), or telling us what the character is doing while he speaks ("he paced across the rug with his arms clasped behind his back"). Adding description to your dialogue will transform it from a dull script to a lively conversation.
All that said, make sure you don't go too far. Description is important, but don't let it overwhelm your plot: who cares what things look like if nothing is happening? The trap many authors fall into is that they add a lot of detail about things they happened to research and think they need to share all of that information with the reader. You don't. Information is good for non-fiction, but fiction needs plot, so when you edit, make sure your plot is constantly moving forward instead of being bogged down with description that your reader doesn't really need to know. This is especially true the first few chapters (hint: the chapters you send as a partial to agents!), where your reader wants to see where your story is going to decide whether they want to continue reading, not the detail of every single noun in the book.
Good luck, authors. Your readers (and especially us interns!) look forward to reading your stories!