Masterclasses are a great and underrated resource.
I went to my first master classes when I went to my first horn workshop (a pretty awesome experience in and of itself) and I still enjoy going whenever I get the chance.
I feel like watching a great teacher work with a student makes me both a better player and a better teacher – no matter the level of the students playing. I remember one of the most educational master classes I’ve been to was watching William VerMeulen work with high school students. You can get a sense of his great pedagogical skill from his 6 Quick Fixes video, but I remember being blown away by how quickly and efficiently he improved their playing.
If you don’t have the ability to go to many master classes in person, though, there are lots of great resources for horn players on Youtube! To make it even easier for you, horn player Ryan Everson has put together a great collection of masterclass videos available on Youtube. You can find great videos with famous names like Jennifer Montone, Stefan Jezierski, Julie Landsman, Eli Epstein, William VerMeulen (of course), and more.