What you want to talk about is just the first step in what you will communicate.
Learning communication skills are important, but just as important is figuring out how you want to say things. Do you prefer one on one, one to large groups, group settings, mentorship, coaching, etcetera?
Are you funny or matter of fact?
Are you verbose or to the point?
Do you use profanity?
Are you motivational or thoughtful?
Are you quiet or outspoken?
These are all hard questions to answer because they are wrapped up in what you do.
It is like peeling an onion. One layer is what you want to do in the world, the next layer is how you want to present it. The layer after that is what you can do in the world based on what you present.
There are always more layers