A combination of two things:Franklin Eddy said:
1) joined a writers' group (the SlugTribe in Austin, Texas -- one of the best if not THE best permanent writers' group; members include 2 professional editors and 3 other professional writers, including major award winners (for example, Year's Best Fantasy Short Story)); and
2) followed Jerry Pournelle's advice -- wrote and threw away a million words of the best copy I could write.