learning how to write is learning how to think. you begin with a problem to solve: how do I express this thought, idea or feeling in a way that best approximates my meaning? what is my meaning? can I refine it? writing is a tool you use to answer these questions.

it follows that good writing will have undergone many revisions. you write, then ask: is that what I really mean? more often than not the answer will be no. so you go back, revise, reread, repeat. if you think it's easy to write what you mean you're not aiming high enough.

so IME when a work is 'not well-written' (this applies mostly to nonfiction) the flaw lies not in syntax or vocabulary or expression, but in a certain incoherence of thought which manifests itself as poorly framed hypotheses, conclusions that don't follow from evidence, etc.

good news is this lack is simple (not easy, simple) enough to correct. mindfully read good work. dissect it to see how it delivers. don't be intimidated, be curious. do it every day until the lessons of those who are so much better than you are part of you. then do it again.

truthfully, you'll probably never be satisfied with the end product, and you'll always second guess yourself. i know. that's okay. so for shorter work give yourself 3-5 revisions. then send it into the world. imperfect pieces are paving the way for those closer to your vision.