Have something to say, study the craft of writing, and communicate as simply as possible.

That last one is key.

No one gets extra points in writing for sounding smart. However, you can change your life if you can communicate clearly but simply.

As for studying the craft of writing, read a lot of books. In all genres.

Too many people sound generic because they only read business books.

Pick up history, science, fiction, etc. Even learn how to read peer reviewed research. You can never stop learning how words are used.

To that last point.

You know that your writing is good if you're able to get ideas to take hold in the reader's mind. It doesn't matter what the idea is.

All that matters is that you gain a piece of their mental real estate.

This is largely a function of having something to say, but you must also craft the message well and in its most simple form.

Or, at the very least, as simply as possible to avoid unnecessary confusion.