Learn WordPress internals. Learn WordPress best practices. Study up on PHP code style and design patterns. Work on learning the devops side of it.
There’s always more to learn about any given tech stack. You can just pick the last part of it that gave you trouble and do some googling.
The market for WordPress development is huge. I could be making double the amount of money I’m making now if I wanted to start my own consulting shop. But I like Rails and I’m making enough money now.