1. You need to write in a way that addresses your goals within the context of a particular situation. I review a good book on the subject here: https://codewithoutrules.com/2016/06/15/writing-book/

2. You need to understand the idea of style: there are multiple styles, each with its own set of assumptions about how you address the reader, what "truth" is, etc.. "Clear and Simple as the Truth" is a great book about the idea of multiple styles, and one particular style (the classic one).

3. Learn the practical style, which is suitable for many business writing situations. "Style: basics of clarity and grace" by Williams and Colomb is great book on the topic.