Good writing is not about impressing readers with your vocabulary. It is about making ideas travel from your mind to theirs with as little friction as possible.
Most advice on writing focuses on mechanics — avoid passive voice, cut adverbs, vary sentence length. These are useful heuristics, but they mistake the surface for the substance. Clarity is not a grammatical property. It is a cognitive one.
A sentence is clear when the reader does not have to re-read it. A paragraph is clear when its logic is self-evident. An essay is clear when you finish it and feel you have gained something, not when you feel you have survived something.
The hardest part of writing clearly is that it requires you to have thought clearly first. You cannot dress up a fuzzy idea in crisp prose. The fuzziness will leak through, no matter how carefully you arrange the words. Revision is largely the process of discovering what you actually think, rather than what you hoped you thought.
Write one true thing. Then write another. Let the structure emerge from the ideas rather than imposing a structure on them prematurely. Outlines are useful, but they are hypotheses about what you want to say, not contracts.