The main way I improved my writing was to take everything I wrote seriously. Whether it was a text to my Mum or a note on the fridge. I would always strive to write it as well as I could. Pretty soon I found I was paying more attention to other people's written English and saw the mistakes I was making.
I'm uneducated. I was expelled from school because of fighting and only came back for a couple of exams. So there's gaps in my knowledge but you can improve when you put the effort in. It's worth it.
Thank you for sharing, this is a great story of how you are the master of your own future.