Complex sentences and uncommon words obfuscate meaning, when they should be conveying. I feel this needless complexity is often treated like country-club dues; you need to use it to belong.

Patrick Henry Winston was well known his achievements in machine learning, but also for his yearly lectures on communication. His book "Make it Clear" is full of great lessons, which have improved my writing/speaking. As basic as it sounds, considering my audience and intent have greatly improved my ability to express my ideas.