1. Revise constantly. If you haven't revised it three times you almost surely haven't done enough. You don't need an outline, but as you write new thoughts will occur to you, previously open questions will be answered, opinions of priorities will shift. Writing in the Rubber Duck school of programming to the nth degree. All that you discover you already knew should be completely reflected in the final document. This is a very painful thing, you can spend hours on something and be "almost done" when you realize the key question on which all depends, the answer to which requires a complete rewrite of the document.
Note that "revision" often means changing the purpose of the document. You can go from reporting status to asking about key variables driving that status. Text may not be the right medium for the new message.
2. Edit ruthlessly. Everything can be shorter. The time you take clarifying and shortening saves your readers that much and more -- since you, not they, are best positioned to solve the puzzles posed by an obscure sentence, and to summarize an overly long one. If your readers number more than one, the time savings are multiplied.
3. Be very clear in your terms, meanings and references. If they aren't clear, explain them. Did that explanation just blow up your document's organization? Time to revise. Be precise. Your audience does not have your perspective -- your local environment variables are not theirs -- you need to orient them to the topic before you can expect casual references to be meaningful.
4. Much business writing requires an imperative style. At the top, tell your reader the action or decision expected / hoped for of them at the end of the document, and tell them what you will talk about. As you provide information, keep it in relation to the action expected of them. If there is no relation, what is it doing here? If it must be in here, why? and what are the implications for the stated purpose of the document? Is it time to revise again?
At the end of the document, give them detailed instructions about what they should do next -- call at this number, email that address, provide these thoughts, whatever.
Good training in writing is available and worthwhile. If you really want to get better, seek it out.