Paul Theroux in the Wall Street Journal on how and why to take notes. Great practical advice for any sort of writer.
The daylong keeping of notes is not the end of the business. Inevitably, the notes are hurried, disjointed, scribbled and abbreviated. Left on the little page, they become incomprehensible with time, and so they must be amplified and made coherent. I do this at the end of the day, or early the next morning, in a bigger well-bound notebook that allows me to write dialogue and substantial paragraphs, with afterthoughts on the facing page.
It usually takes hours to write the account of a day, anywhere from 1,000 to 2,000 words (and often more). It is best done at meal time in the evening at a well-lighted table in a quiet corner, or under a tree in the morning. It's the summing up of a day or a significant encounter, enlarging on notes done on the fly while they're still fresh enough that the suggestions in them help to recall detail.