Communicate With Authority
In WA training, Kyle mentions, many times, to write "conversationally". Upon review, I find web post that sounds "casual", instead.
Webster defines "conversationally" as, "an exchange similar to conversation." In other words, it's how you'd talk to a friend. You wouldn't be "careful". You'd speak, freely. Let it all hang out. Another word for this is colloquially- an oral exchange of sentiments, observations, opinions, or ideas.
"Casual" on the other hand means, 1. Feeling or showing little concern : nonchalant, 2. Lacking a high degree of interest or devotion, 3. Done without serious intent or commitment.
I believe, if you want to be "Authoritative" in your work, be conversational, just as Kyle said. To be authoritative is to be "clearly accurate or knowledgeable".
(Did you want an English lesson?)