For myself, this almost always leads to a better discussion, or at least a better understanding on my part.
It also takes the pressure off, because I often don't know what I'm talking about.
I also strongly disagree with expanding your vocabulary, unless you're a non-native speaker. "Big words" have been shown in studies to make your writing harder to understand and seem more pretentious. Good writers can express themselves in a way that an average person can follow.
Same goes for perfect syntax: language is fluid and evolves, and breaking the stricter rules can be very effective.
Personally I’ve spent > 10 years arguing with strangers on the internet. It can be a fun way to pass the time, I think many here would agree. I believe I’m a lot more effective now than I was years ago. I think you have to be aware of concepts and definitions, not only how you think of them but how the other person thinks of them, so you can argue in their terms, yes this implies active listening or reading, as you indicated. Also being able to explain things in multiple ways.
Finally, I think the onus is on me to make myself understood, not on the reader to understand me. This can be a subtle distinction many fail to realize. If you ever find yourself saying “you didn’t understand me” then chances are you have some work to do.
My two cents: know what you want to communicate, don't deviate from it. Organize your writing or speaking like this: 1) tell them what you're going to tell them, 2) tell them, 3) tell them what you told them. In other words, have an intro, subject, and conclusion, even if you're only writing or speaking 5 sentences. Speak slower, allow pauses, that way you can think through things.
1. Introduction: Tell us what you're going to say.
2. Body: List your facts, create a sub-list of those facts that you are going to argue from, argue from them, undermine yourself by introducing the facts you weren't going to argue from and explore how adopting those changes your conclusion, explain why you chose to exclude those other facts to begin with and thus invalidate the counter-argument (while have shown yourself to be receptive to it).
3. Conclusion: Tell us what you said, and tell us how one could go about settling controversies that arise between yourself and somebody else who reached a different conclusion.
I'm still not excellent, English is my second language and I often do make mistakes, but I've made huge progress simply by reading and writing a lot.
Also, some people will disagree, but I think that tweeting is a very fun and productive way to practice concisely articulating your thoughts.
You can also combine these ideas: listen to audiobooks, take notes, and share the most insightful things you've learned on twitter or blog.
I read most of those books in middle school, but prior to that in elementary school, I was already reading at a 12th grade level according to some reading test we took in school.
As to why my reading comprehension was advanced for my age? No idea.
I don't nearly do as well with public speaking, but I've tried Toastmasters for a while, and think that helps. At the minimum, you'll meet some great people, have some fun, and listen to (and share I hope!) some great stories.
Next time someone asks you a question, think “When is that true? When is that false? What are the ddpendencies of true? What are the dependencies of false? Is true and false the only option? Under what conditions?”
Once you have answered all these questions in your head, then you may answer
You’ll get faster and faster at it
For example if I know I need to explain Blockchain to someone I would sit down before-hand and write a simple explanation, rehearse it until I memorize it, then I would explain it to the person, the first time I explain it I might be slow and rusty, but if I have to explain it to another person I will be a bit better, etc. etc. so by the time someone else asks me to explain it, I sound like a genius :)
This can apply to Technical, Scientific, Personal, and any kind of content/concepts really. You can use this practice to improve your social skills too and tell interesting stories!
Also, not clear what you mean exactly. In writing? speaking? Two entirely different things. Some can do both, neither, or one of those well. Well, more than two; there are a wide range of forms of both.
[0] https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect
With that said, practice writing down thorough explanations of things, then play with the way that you've structured or presented the statements. Think about how a reader/hearer might respond to what you've said. Then practice what you've learned by communicating with friends/contacts.
Also, speak slower.