Picture your audience. Outline. Review. Scramble to produce the first draft. Don't edit heavily as you write. Get it done. Know that you're putting in too much at some points and too little at others. The addition and subtraction will come later. Be especially wary of anything which is clever. When the first draft is done, check for tone, order, and flow. Above all, check for clarity. Write another draft. Then another and perhaps even more. Learn how to write quickly without becoming impatient. Impatience fosters mistakes. [You'll make enough mistakes without it.] Impatience can cause you to ignore alarm bells.
Not there yet? Write another draft.