Avoid Adverbs: This one is simple: delete your adverbs. If you’re not sure what an adverb is, the easiest way to identify them is that they frequently end in “-ly.” This is, again, more about pruning than outright abstinence: you can still use adverbs, but save them for when they mean something.
Avoid Repetition: If you use a less common word too often, your writing starts to sound odd. When writing, and especially when editing, make sure you aren’t using the same word too frequently. Don’t repeat an uncommon word in the same sentence, ideally not in the same paragraph, and possibly not for the rest of the section.
Vary Sentence Length: Most of us speak in longer or shorter sentences, and that will tend to come through in our writing. But if you monitor the length of your sentences, and force yourself to make some of them shorter or longer (depending on which you default to), you’ll make your writing sound more interesting. I like long sentences. But a short one every now and then helps make my paragraphs more readable.