A couple of years ago, I signed up for Garner's Usage Tip of the Day, a daily e-mail containing one or more selections from Garner's Modern American Usage, with a bonus pithy quotation. Several months ago, the e-mails stopped. But just a few days ago, they re-started. You can subscribe by clicking here.
Yesterday's bonus pithy quotation is an excellent digest of the writing process, applicable to any form of expository writing:
We should "first think, and then write": think till we have thoroughly assimilated our materials and have determined what we would say, and then write as rapidly as possible, with minds not occupied with choice of word or turn of phrase but intent on the subject. After the first draught has been made, we may at leisure attend to matters of detail, criticise from various points of view, curtail here, amplify there, until each part has its due proportion of space and effectiveness; but unless we have a conception of the whole before beginning to write, and unless we write with an eye to that whole, there is little likelihood that our work will be a unit.
— Adams Sherman Hill, The Principles of Rhetoric 243 (rev. ed. 1896).