Ed Whitney said, "Decide the essence of a thing - then explain it with the fewest possible strokes."
Ernest Hemingway said, "You can leave out what you know, but you can't leave out what you don't know."
[Many instructors say, "Simplify, simplify!" -which is good advice, but my experience has been that, starting out, at least, I had to put EVERYTHING in including the KITCHEN SINK to learn, only gradually, WHAT could be left out. The KITCHEN SINK might, of course, turn out to be the best thing in the composition.]
This idea, seen from another angle, was told to me by a friend who used to laugh himself silly telling me, "An old lady, when asked what she meant, said: 'How do I know what I MEAN until I've SAID it?'"