Why Writing is Essential for Better Thinking
Writing is an essential skill to acquire. Even if you don't plan to publish anything, writing is important because it helps you to clarify your thinking and discover weak spots in your reasoning.
Writing is, without dispute, the best facilitator for thinking, reading, learning, understanding, and generating ideas we have.
— Sönke Ahrens, How to Take Smart Notes
When you grab a pen or sit down at your keyboard to explain an idea, many times you'll discover that you don't understand it as well as you thought. Also, there are some things about any subject that you don't consciously realize until you have to explain them. While you could do this by talking, writing the explanation forces you to think things through. "You think you have fully formed ideas, but when you try to put them into words you discover that you don't[^fully-formed-paul-graham]."
[^fully-formed-paul-graham]: cfr Paul Graham, Putting Ideas Into Words.
Writing is also a way to come to new ideas. When writing about something, many of the ideas will be ideas you thought of while writing.
By doing everything with the clear purpose of writing about it, you will do what you do deliberately. Deliberate practice is the only serious way of becoming better at what we are doing (cf. Anders Ericsson, 2008). If you change your mind about the importance of writing, you will also change your mind about everything else. Even if you decide never to write a single line of a manuscript, you will improve your reading, thinking, and other intellectual skills just by doing everything as if nothing counts other than writing.
— Sönke Ahrens, How to Take Smart Notes
YCombinator founder Paul Graham has a more radical take on writing: "If writing down your ideas always makes them more precise and more complete, then no one who hasn't written about a topic has fully formed ideas about it. And someone who never writes has no fully formed ideas about anything nontrivial. (...) Not only won't you have fully formed ideas. You'll never realize it[^pg-idem]."
[^pg-idem]: cfr. Paul Graham, idem.
To get better at writing, you need to... write. Make it a daily practice. Better if you do it in public because the stakes are higher and it will help you commit to the practice. You can open a blog today and start writing about your favorite topic. Use a pseudonym if you prefer.