Start with the basics. Read a business writing book, articles, or take a course on it. Even a one-hour course will teach you something new. Beyond that, some things that help me address my weak spots:
1. Make sure your first paragraph or executive summary answers the questions: Why does this doc exist? Who is the expected audience? What actions or decisions does the author expect from the audience after reading the doc?
2. Run things through an analyzer like Hemingway[1]. It'll point out obvious things to fix.
3. Do a reverse-thesaurus editing pass. Remove adjectives and flowery language where possible. Challenge yourself to lower the reading level. Even if your audience has PhDs they'll read and comprehend simple language faster.
4. Do an editing pass for missing numbers. Vague language, unsupported assertions, and missing quantities make arguments easy to refute. Look for words like "many", "most", "a lot", "major" "severe" "large" and replace them with hard numbers where possible.
5. Do an editing pass for "So, what?" and remove anything that isn't necessary to support your core argument or purpose. Assume your audience is smart but has very little time. Too much detail will make them start to skim and miss things. Appendixes are your friend here. Leave links to appendixes for readers that have questions or want more detail.
6. Nothing beats a human reviewer. Professional writers have editors too.
[1] http://www.hemingwayapp.com/