Try publishing something to a public blog every day (even if it's under an alias). It doesn't have to be long, but by intending to publish something you'll be forced to edit, rewrite, and eventually settle on a way of writing something (if you don't settle, you'll never be able to press publish—this is where publishing daily helps). Over time, you'll be able to revisit old posts and see how your writing has changed, and you'll be able to learn from previous writing.
I've published more than 1,700 posts to my personal blog over the past 16 years and I've found that the greatest improvements to my own writing have come when I was blogging regularly (comparing posts from one year to another makes this very obvious). Whenever I've stopped blogging regularly for long periods of time, I've found that my writing stops improving, even if the overall amount of writing that I'm doing on a regular basis hasn't changed that much.
I'm not saying that you cannot improve as a writer when you write privately, just that improvement requires working toward specific goals that you know will challenge you to improve. Write a haiku. Write a short story. 487
Look up from your laptop, find an object, and then try to write 500 words describing that object in as fine detail as possible. Do the same thing with an emotion that you've felt. And if you can, share what you write. Even if others don't give you feedback, the very knowledge that somebody, somewhere, will likely be judging your writing will cause you to subconsciously work a little harder to write better, to rewrite and to edit (which is the work that actually produces good writing).
When writing comments or posts online, push yourself to spend a little extra time editing and rewriting—use every opportunity to practice the craft.
Remember: everyone, no matter how famous, had to learn how to walk. They had to fall down and get back up, fall down and get back up, until they learned how to walk. (And even then, we still slip and fall from time to time.) The same way, every writer, no matter how famous, failed and wrote badly before they learned how to write well. 487