Write quickly. It makes writing flow, makes writing conversational and stops you overthinking* (*trying to be too clever).
Write accurately. Not just in getting the facts right, but also in not being sloppy with the meaning of a word or a phrase. And in re-writing an idea again and again until it expresses precisely what you mean not just something like what you mean.
Write as yourself. Don’t try to write like someone you admire. If you tried to talk or dress like them you’d look like a fool. Same applies. (Don’t use Americanisms if you’re not American.)
Keep your ambitions high. Don’t write to be good enough, write to be the best you can be. If the metaphor is just okay, ditch it and write plainly instead.
Write with variety. Vary the length of sentences. Vary the construction of sentences. Vary your perspective from the immediate to the bigger picture.
Don’t show off. (Don’t use Americanisms if you’re not American.)
Write clearly. Don’t write like you’re writing an essay, using complicated sentences and long words to give the impression of intelligence. Write things as plainly and directly as possible. Pay attention to word order. The words are steps on a path; if they’re in the wrong order people will get lost. Pick them apart and put them back together in the right order.
Write efficiently. Cut out all the extra words – there’ll be plenty of them hiding in there.