[marcusverus]

This should absolutely be the first stop for anyone who wants to improve their writing. Just don't get bogged down in the more narrowly-focused chapters, like Chapter 13: Writing About Places: The Travel Article.

Another helpful book is A Rulebook for Arguments by Anthony Weston. It focuses more on the organization of your thoughts before you start writing. When writing about more complex topics, I frequently find myself discovering what I want to say as I'm writing, which makes for a lot of re-organizing and re-writing and wasted time. By slapping together an outline of what I want to write before I get started, I can identify what I want to say--and the optimal order in which to say it--before putting pen to paper.