On writing well...

My first few years of graduate school were a constant struggle. I quickly discovered that just writing down my ideas was not enough. To succeed as an economist, I had to write clearly. In paper workshops I would repeatedly hear comments that the readers did not understand the argument or how the sections of my writing related to one another. The work would have flavor but they couldn't tell what it was. Recently I've been told that my writing and clarity has improved. I attribute this to two factors. First, writing and revising more often. Second, reading material on the topic of writing. For the second, I recommend the following:

Books:
On Writing Well by William Zinsser
The Elements of Style by Strunk, White, and Angell
On Writing by Stephen King

Articles:
How to Write with Style by Kurt Vonnegut
12 writing tips by George Orwell