Write freely and as rapidly as possible and throw the whole thing on paper. Never correct or rewrite until the whole thing is down. Rewrite in process is usually found to be an excuse for not going on. It also interferes with flow and rhythm which can only come from a kind of unconscious association with the material.
Based on my experience with Celebrated Summer (1989) I completely agreed. I would have been much better off if I had kept up the momentum I had in 1997 and gone all the way to the end. Instead, I abandoned the novel until 2001 and then got stuck in 10 years of rewriting Part I over and over.