Medium is a great place to start. In fact, I have a group that shares each other’s Medium posts every Monday. If you’re on Facebook, feel free to join us!
The key to growing as a writer is really threefold:
1) Write every day if you can. Practice makes you better. Post some of it here on Medium. Once a week is a good target. If you want to post more, go for it!
2) Sharing ups the ante. Join a group of writers, whether it’s mine or someone else’s. It’s a great way to learn and grow.
3) Make a few friends who are writers. Commit to check in at regular intervals to share your writing accomplishments and progress. I’d say make it at least weekly.
That should get you started. As you get more comfortable, start asking publications on Medium to let you write for them.
One final tip: pick one topic you’re passionate about and start writing.
Have fun! And be sure to come back here and share the link to your first post.