The very first thing to do is find people better at writing than you who will offer critique. There are in-person writing groups in your area.
https://www.meetup.com/topics/creative-writing/ca/on/toronto/ These are typically quid-pro-quo; be prepared to have to read other people's writing and give them your own thoughts, too. Additionally, many moons ago our very own Glen used to run a writer's workshop. You can tell because of the high quality of his eviscerations here. Maybe send him a PM. I know TVC also used to write so he might have some advice.
The key to writing is reading. Read something much more difficult than you're accustomed to. Become sensitive to the way authors organize their writing, both in the large and the small. As you progress as an amateur writer you will become increasingly aware of the skills that others have and you will assimilate that into your own repertoire.
Learn to edit. Before you even go to a workshop or bother someone else, you should have gone over your own work and fixed it the best you can, preferably some time after you had originally written it. Listen to the most critical part of your inner voice. If you think you haven't done a good job in a spot, you're right.
Write a lot. Set aside time for it as a real hobby. If you set a consistent time for it every day then you'll develop a routine. Don't just write when you feel like writing. It takes something like 20 minutes of continuous concentration before you really start focusing on a task. Those ideas that you're sitting around waiting for have to be chased. And make sure to outline.
Learn the rules. Do not break the rules until you have become good with them - you are not Samuel Beckett.
