Values
Two of the most important qualities of a book: Humanity and Warmth. It's about using the English language to achieve the greatest clarity and strength.
Writing is a craft, you need to establish a daily routine and stick to it. A man who stops writing because he lacks inspiration is fooling himself, and will go broke.
‘the self who emerges on paper is often more stiffer than the self who emerges to write’
Style
Don't make the mistake of taking simplicity to such an extreme that you lack any style ('Dick likes Jane', 'See Spot Run')
Be yourself, be confident, relax. Write in an honest way with words that come naturally.
Writers who deliberately garnish their prose cause them to lose what makes them unique, because the reader will notice that you are faking. People are connected if they know a human is writing. It's wonderful to have a day when you're reading and exclaim: 'Aha! A person!'
Audience
Write words and ideas that solely please yourself (E.B. White writing about Chickens, H.L.Mencken condemning Christian pieties with his 'pyrotechnical use of the American Language'). However, make sure to work hard to master the objective tools of writing (clarity, knowledge of material, grammar) for the reader.
Never say anything in writing you wouldn't feel comfortable saying in conversation. You're probably not a person that says 'indeed', 'moreover' and 'individual' ('he's a fine individual', don't).
Words
Bear in mind the sound and rhythm of your words, readers hear what they are reading far more than you realise.
Get yourself a thesaurus and use it frequently. Learn the difference between 'coax', 'cajole, 'wheedle'.
Writing is learned by imitation. To get better at writing, read the men and women who write the way you want to, and figure out how they did it.
Paragraphs
Keep your paragraphs short (with exceptions). Writing is visual, short paragraphs are inviting, long paragraphs are intimidating.
Don't go overboard though, only split a paragraph if needed. A succession of tiny paragraphs (like with many newspapers) is as annoying as a paragraph that's too long.
Great nonfiction writers always think in terms of paragraph units instead of sentence units.
Rewriting
The first draft is often bad. It's always wordy, not clear, pretentious. Rewriting a draft is where the battle is won or lost.
Rewriting doesn't mean writing a different second version, it mostly consists of reshaping and tightening your first draft.
Keep putting yourself in the reader's position and find places where you might lose the reader or more things they need to know.
It's a delight to delete entire words, sentences, paragraphs, of dull or unnecessary writing.
Methods
Source:
On Writing Well(Book), Chapter 1, 4-10