These kind of injunctions do more harm that good, I think. Style is incredibly variable, changes with the tides, and rarely follows any well defined set of rule

These kind of injunctions do more harm that good, I think. Style is incredibly variable, changes with the tides, and rarely follows any well defined set of rules. I've always resonated with the way Robert M. Pirsig describes it in Zen and the Art of Motorcycle Maintenance – good style is hard to nail down, but you know it when you see it. Better to show your students examples of (what you consider to be) good writing, hone their instincts as to what makes an enaging read, and get them to write as much as possible, in as many ways as possible.