I think the best I can do here is my usual answer: take some time every week to work on a problem that is a little bit harder than what you already know how to do. It requires discipline, and it's hard, but it reliably results in levelling up.

It also helps with humility: if you're constantly working on things that are too hard for you to do, it's hard to build up an unhealthy belief in your own abilities. And humility will keep you open to unexpected learnings from collaborators and people working on related things.