Confidence. Even if you know that the other people know better, your sheer confidence alone can make them doubt themselves. Fake it first, and then it becomes natural

Each of us is the centre of our own little world. When we speak it is of no value except to the person listening[1]. The collision of these two facets creates most of the problems. Without going into to much detail, what your listener needs should be your first and often only concern. All too often people speak based on what they themselves need. As an example if you are talking to a group you know well, you may still have a need in yourself to break the tension, something they don't need, so to do so is self serving.

Obviously in, say, an interview you need to give a good impression. I am counting that as what the listener needs.

[1] sometimes what you hear yourself say can be relevant, but rarely!

Record a video where you talk about any topic in one shot, watch it, be embarrassed of how bad it is, repeat until you're not embarrassed. Extra points for publishing the video on YouTube.

Look at your favourite presentations / speakers on YouTube, try to copy what they do.

I'm a horrible communicator, but these are some tips that have helped me:

1. Give the conclusion first, ramble the details after so people don't get lost.

2. Only share something if it impacts decision making, otherwise it's just noise.

3. Prefer arguments based on facts, because "I don't like it" is too vague for others to make decisions on.

Bless you for your noble intentions.

I’m not sure I have helpful advice for you, though I appreciate your observation and desire to improve in such an away.

We learn best by example. If you could find the writings of someone who’s way of speaking impresses you, even fiction, reading their words out loud may inspire your mind to optimize for this sort of communication style.

I do something similar for learning to speak for other purposes (story form, I like to tell stories orally.)

Your intention is a good one!