Learning how to practice. I'm going through some rather rigorous hands-on training where more than half of the students end up failing out. It distresses me to see everyone wasting a full hour running an entire problem when the particular action they actually need help on takes 10 minutes, tops. Practicing efficiently is one of the best things my father taught me. Graduate+ level musicians are bound to have great tips for this. Of course, effective studying is in many ways similar, but it seems more intuitive. That is, no one could possibly be stupid enough to study for a literature exam by sitting down reading the book cover to cover several times.
So, transferable skills: skills that, upon improvement, increase your ability in other areas (and also improve other, higher-level skills).
A basic example would be reading/writing. Knowing how to read and write allows one to access a huge amount of other skills and resources which are otherwise unavailable. A less obvious example would be clear speech (enunciation). Ability to speak clearly improves one's prospects in a lot of different areas (e.g. professional advancement, dating, etc.).
I'm looking for additional examples. Which skills did you find to be most transferable? Did you become proficient in X, and then found this helped you in many other areas of your life? Please share.
(I tried to find whether this was discussed before, and failed; if it was, I would appreciate the link.)