In her wonderful paper on how to research well and write clearly, Deirdre McCloskey suggests that we always carry with us a pack of 4 by 6 cards, so that we have them handy when we are hit by an epiphany or hear a relevant quote. (The suggestion probably also appears in the later book versions of her wonderful paper, but I do not have a copy handy to check.)
(p. C11) Mr. Chernow usually spends about twice as much time researching a book as writing it. He types up his research on a computer, so that he has it backed up, and then prints out the individual entries on paper with perforated edges that he can tear into 4-by-6-inch cards. (He was inspired to use index cards by Vladimir Nabokov, who wrote his novels on them.) He then files the cards chronologically and indexes them. His research on Grant fills some 25,000 cards packed into 22 boxes, all stacked up in the office of his Brooklyn brownstone under a big abstract painting.
For the full interview, see:
(Note: the online version of the interview has the date Sept. 15, 2017 [sic], and has the title “WEEKEND CONFIDENTIAL; Ron Chernow’s New Chapter: Ulysses S. Grant.”)
The main Chernow book discussed in the interview is:
Chernow, Ron. Grant. New York: The Penguin Press, 2017.
McCloskey’s wonderful paper, mentioned above, is:
McCloskey, Deirdre. “Economical Writing.” Economic Inquiry 23, no. 2 (April 1985): 187-222.