100 Ways to Improve Your Writing (Updated): Proven Professional Techniques for Writing with Style and Power

The best-known one is Thirty Days to a More Powerful Vocabulary by Wilfred Funk and Norman Lewis. Read that book or one like it.

Writing should be conversational. That does not mean that your writing should be an exact duplicate of speech; it should not. Your writing should convey to the reader a sense of conversation.

Readers will like you if you show that you are human. In a how-to piece, for example, you might write, “This third step is a little hard to master. I ruined six good slides before I got it right. So be smarter than I was; practice on blanks.”

You cannot write securely on any subject unless you have gathered far more information than you will use.

So write with a combination of short, medium, and long sentences.

take a few deep breaths, put your pulse rate into second gear, and deliver a supply of oxygen to the brain.

Strive instead to write well and without self-consciousness.

For the writer of average intelligence and education, learning new words is much less important than learning to use easily the words he or she already knows.

do not pour the clay of your thoughts into the hard mold of some personal writing style that you are determined to have.