Just like anything else, becoming a better dresser takes time and practice.
One thing that people continually forget is that in understanding the rules of style and becoming more comfortable with proper fit, it takes a lot of trial and error. And it's completely okay.
During my "style improvement journey," I can think of one too many times where I dressed pretty sloppily, wearing overtly baggy jeans or old T-shirts that were three sizes too large. As time went on though, I started shedding those pieces in favor of more fitted and attractive clothing. It was a process (one that took years), and I'm still not at the finish line, nor do I expect to be anytime soon. It's a learning process, one that takes a lot of patience and perhaps some risk.
Also, I know I'm definitely not alone in going through it.
In this moment, I can think of two amazing menswear icons that have had quite drastic style evolutions in the past decade: Andre 3000 and Daniel Craig. Check out those links to see how their style has changed over the years.
To be frank, these folks clearly did not know what they were doing even as recently as a couple years ago. However, they continually experimented, sometimes wearing embarrassing and ridiculous clothes along the way, ultimately evolving into the excellent dressers they are today.
So in all, don't be afraid to take some risks and even make mistakes in this process of dressing better. We all go through it, and it will only help you make wiser decisions as you move forward.