Don't waste the reader's time. "If I had more time, I would have written a shorter letter" - Blaise Pascal.
The look makes a difference. Make your text easier on the eyes. Use bullet points, white space, shorter sentences, margins, boldface, etc .
Be smart: don't try to sound smart. Avoid jargon.
Be the authority: don't use "I'm thinking", "in my opinion", etc.
Scaffold well to write well. Structure you text in 3 phases: say what you want to say, say it, repeat it.
One idea per paragraph
Every paragraph should start with a strong sentence on the paragraph's topic.
Start with your purpose, not the motivation or justification for it.
The text may become too mechanical after revising. Keep your "voice" in your document by reading it out loud.
If you find duplicate sentences, cut out the negative sounding ones first.
Grammar matters.
Grammar - I vs me: use I if it's a subject
Attribute modifiers like adjectives need to one of the nouns. Make them adjacent.
pronouns are words that take the place of nouns, like I, he, them. They refer to the closest antecedent noun.
Think of the writing from your reader perspective
Cut adjectives and adverbs; qualifiers and amplifiers; “in fact”, “possibly”, “generally”, etc
Cut out generalities like "everyone knows", they often include the words: all everybody, everywhere, etc. You may need to rewrite sentences to make them more specific if they include words like: some, somebody, etc.
use an active voice: "Bob did X", not "X was done by Bob". Passive voice is longer, less clear, and less emphatic. But it's acceptable in scientific papers because it sounds more impartial.
Limit verbs "to be" and "to have". Including forms is, am, are, were, was, will be, have, has, had, have been and more.