I have 100 blogs and have written for 10 years in my language (Persian), but I'm not focused on increasing my ability to write better.
What exercises should a writer focus on when blogging to be a better writer?
How can I use comments and feedback from readers of the blog to improve?
What practices should an amateur writer adhere to in order to gradually become a professional?
Writing a lot is good for writers.
The more you write the better writer you become. No matter what you write. If you write blogs, that's just fine.
Still, there are problems no amount of writing will help - just opposite, it will make them rooted harder. If you keep making a certain mistake, lots of writing won't help against it. Lots of reading may help. Writing exercises. Using proofreaders of your texts for more than just correctness - but for learning your own mistakes. Trying various styles and new approaches. Experimenting in creative writing and taking honest criticism.
...not even getting started on the ugly business side of writing professionally. Learning to write what you believe is wrong but what the publisher believes is right, and so on.
Yes, blogging will help you become a professional writer.
No, blogging will not make you a professional writer. It's useful but it's not enough. You need other exercises besides that.
Writing a blog may be less useful than reading the work of others and analysing what they have done and why.
Ask yourself "Would I have written that in that way?"
While you do want to develop a distinctive style that is not simply a copy of everyone else, individuality is no justification for repeating the same errors.
