This is more of a meta skill, but "learning to learn" was a game changer for me. For a long time, I had approached learning in a set and done kind of way, i.e. I'd read and immerse myself on a new topic, declare I'd learned it and move on. But I realized that was not only wrong, but it was blinding me to my shortcomings. I took a few courses, and started testing myself regularly on new topics to overcome that blindspot. YMMV!