The New York Times Writers on Writing series focuses on fiction, but Elmore Leonard’s “Easy on the Hooptedoodle” (free subscription required) has a rule every writer should obide by, regardless of genre:
Try to leave out the part that readers tend to skip.
Too often when I edit a document it hits me that I’m probably the only person who will read a particular section. I often wonder if most readers, executive or lesser folks, get past the executive summary. Authors should consider the amount of documents their audience receives and keep that in mind when writing. Better to be brief and read than detailed and deleted.
Editors, of course, don’t have the option of skipping parts.