The Guardian asked a series of writers, including Elmore Leonard, Neil Gaiman, and Margaret Atwood, to list their writing Do’s and Don’ts. Hard to pick a favorite, there are just so many that I love, but here’s an example:
Never use a verb other than “said” to carry dialogue. The line of dialogue belongs to the character; the verb is the writer sticking his nose in. But “said” is far less intrusive than “grumbled”, “gasped”, “cautioned”, “lied”. I once noticed Mary McCarthy ending a line of dialogue with “she asseverated” and had to stop reading and go to the dictionary.
Though these rules are all listed by novelists, worth reading by anyone who creates prose of any kind.