So I decided to try to write the book I wanted to read. I wasn’t at all sure how to go about it. One evening, in New York, at a gathering of writers and historians interested in the West, my boss, Alvin Josephy, pointed to a white-haired man across the room. He said, That’s Harry Drago. Harry Sinclair Drago. He’s written over a hundred books. I waited for my chance and walked over. Mr. Drago, I said, Alvin Josephy says that you’ve written over a hundred books. Yes, he said, that’s right. How do you do that? I asked. And he said, Four pages a day. Every day? Every day. It was the best advice an aspiring writer could be given.

And, on avoiding the trap of the Whig Interpretation of history:

Thornton Wilder talked, in that Paris Review interview, about the difficulty of recreating the past: “It lies in the effort to employ the past tense in such a way that it does not rob those events of their character of having occurred in freedom.” That’s the difficulty exactly—how do you write about something that happened long ago in a way so that it has the openness, the feeling of events happening in freedom? How to write solid history and, at the same time, give life to the past and see the world as it was to those vanished people, with an understanding of what they didn’t know. The problem with so much of history as it’s taught and written is that it’s so often presented as if it were all on a track—this followed that. In truth, nothing ever had to happen the way it happened. Nothing was preordained. There was always a degree of tension, of risk, and the question of what was going to happen next. The Brooklyn Bridge was built. You know that, it’s standing there today, but they didn’t know that at the start. No one knew Truman would become president or that the Panama Canal would be completed.

From a marvellous Paris Review interview with David McCullough.