Style: Lessons in Clarity and Grace is the best book on writing that I have ever read. Strunk & White is, of course, great, but their principles are not as applicable as that one. Flexible, but too hard for beginners.
The first lesson is to have confidence: It’s good to write clear, and everyone can do this.
Why writing is hard: The difficulty comes from the fact that readers and writers know different things. Writers know more, so they are susceptible to a false belief that their writings are clear.
The pragmatic approach: So we need to perceive how readers respond to our prose, and adjust our words to better serve them. That process needs carefully revision. But not in the drafting phase. At that time you just write everything, and you get a version that is complete. Then you start your revision and make it better. This method is called iterative refinement.