Writing is thinking on paper. Anyone who thinks clearly should be able to write clearly-about any subject at all.
William ZinsserMemoir isn't the summary of a life; it's a window into a life, very much like a photograph in its selective composition. It may look like a casual and even random calling up of bygone events. It's not; it's a deliberate construction.
William ZinsserTips can make someone a better writer but not necessarily a good writer. That's a larger package - a matter of character. Golfing is more than keeping the left arm straight. Every good golfer is a complex engine that runs on ability, ego, determination, discipline, patience, confidence, and other qualities that are self-taught. So it is with writers and all creative artists. If their values are solid their work is likely to be solid.
William Zinsser