I'm still reading On Writing Well, by William Zinsser. Today's excerpt:
Readers want the person who is talking to them to sound genuine. Therefore a fundamental rule is: be yourself.
No rule, however, is harder to follow. It requires writers to do two things that by their metabolism are impossible. They must relax, and they must have confidence.
Telling a writer to relax is like telling a man to relax while being examined for a hernia, and as for confidence, see how stiffly he sits, glaring at the screen that awaits his words. See how often he gets up to look for something to eat or drink. A writer will do anything to avoid the act of writing. I can testify from my newspaper days that the number of trips to the water cooler per reporter-hour far exceeds the body's need for fluids.
The best way to sound genuine in your writing is to write constantly. It's like anything else in life that you practice: playing piano, baking, drafting blueprints, etc. The more you do it, the better at it you'll become.