I agree with this, though since there are probably lots of fiction-writers here as well, I want to point out that for fiction the advice is somewhat different. In fiction, you'll want to replace adverbs with something longer, because an adverb is telling and not showing, and you need more words to show something than to to tell something.
To quote Techniques of the Selling Writer:
Whenever practical, substitute action for the adverb.
"Angrily, she turned on him"? Or, "Her face stiffened, and her hands clenched to small, white-knuckled-fists"?
"Wearily, he sat down"? Or, "With a heavy sigh, he slumped into the chair and let his head loll back, eyes closed"?
Vividness outranks brevity.
At least, sometimes.
This isn't always a bad guideline for non-fiction writing, either. Telling requires the reader to rely on your authority; showing lets them see for themselves. Compare just saying "biologists romanticized evolution" with giving an example of insects defying biologists' expectations by turning into cannibals.
Of course, on some matters you should just state an issue with your authority and get on with it. If you're explaining confirmation bias, no point in launching to a digression about how and why the brain is composed of neurons. Skip that, or if writing online, just provide a link.
Vividness outranks brevity - at least, sometimes.
The topics of rationality and existential risk reduction need their own Richard Dawkins. Their own Darwin. Their own Voltaire.
Rhetoric moves minds.
Students and masochists aside, people read only what is exciting. So: Want to make an impact? Be exciting. You must be heard before you can turn heads in the right direction.
Thus, I've decided to try harder and actually put effort into the quality of my writing instead of just cranking stuff out quickly so I can fill in inferential gaps and get to the cutting edge of the research subjects I care about.
That's why I asked LWers for their picks of best nonfiction writing on Less Wrong.
It's also why I've been reading lots of good science writing, focusing on those who manage to be exciting while covering fairly complex subjects: Dawkins, Sagan, Gleick, Zimmer, Shermer, Ramachandran, Roach, Sacks, Hawking, Greene, Hofstadter, Penrose, Wilson, Feynman, Kaku, Gould, Bryson, Pinker, Kurzban, and others.
I've also been re-reading lots of books and articles on how to write well: Keys to Great Writing, Style: Lessons in Clarity and Grace, Elements of Style, On Writing Well, The Classic Guide to Better Writing, The Book on Writing, Telling True Stories, Writing Tools, Ideas into Words, The Chicago Guide to Communicating Science, A Field Guide for Science Writers, Six Rules for Rewriting, Writing, Briefly, and Singularity Writing Advice. (Conversations with Eliezer also helped.)
I don't know if I can become the Voltaire of rationality and existential risk reduction, but it seems worth a shot. Every improvement in writing style is beneficial even if my starry goal is never met. Also, it appears I produce better writing without really trying than most people produce with trying. (If you've ever had to grade essays by honors English seniors, you'll know what I mean.) I expect to gain more by striving where I already excel than by pushing where I have little natural talent.
(I won't try to write everything well. Sometimes I should just crank things out. To be honest, I didn't spend much time optimizing this post.)
My other hope is that a few other writers decide they would like to be the Voltaire of rationality and/or existential risk reduction. May this post be useful to them. It's a list of recommendations on writing style pulled from many sources, in no particular order.
And, just one piece of process advice. Do not apply any of these rules while drafting. Instead, write down whatever horrible shit comes out of you and do it quickly. Then revise, revise, revise.
Now: What are your favorite pieces of writing advice?