I was in a very similar sitution as you. I averaged 212-215 the last few years but have raised my average to 226 this year and it really took a concerted effort. What I did was focus on my weaker parts of my game to try to improve them.
I worked on tempo, maintaining perfect balance before and after the shot, keeping my head still but staying aggressive. I also worked on the mental side of it because, you're right, much of it is mental once you have the skills. Exact pre shot routine with intense focus on every shot has helped me, same positive thoughts, regardless of the results.
Every shot carries the same importance, whether you're going for 10 in a row or coming off 3 open frames. Clear your head and refocus every shot.
I also have become better at reading the lanes and making adjustments by watching other bowlers, not just yourself, and stay ahead of the changing lane conditions regardless of how your bowling.