If you want to be credible and authoritative, aside from actually knowing your stuff (which is, of course, foundational) the second most important aspect is to make sure to use your voice and get out there consistently. Be visible, be audible, and be present. So many folks silence themselves on issues they're passionate about, when they have opinions, views and insights that could be incredibly helpful to others if they spoke out. Be one of the ones to speak up: on LinkedIn, on Youtube, and volunteer to speak in public.
You can't tell an audience you're credible - you need to *show* them. Over and over!