on writing well
Chris Blattman has a great post on writing essays, including a link to Henry Farrell's wonderful piece on writing for political science. Farrell put his essay up as a PDF with a creative commons license and I will be referring students to it as research paper deadlines approach.
If I had to pick one of his point to emphasize, it would be this: get to the point. Essays that begin, "Man has fought man in conflict since the dawn of time" or otherwise state the obvious drive most professors crazy. Good writing gets to the point, has clear organization, and shows that the researcher had an original thought or two.