Stop trying to jump to the sexy stuff first

This is very good advice, even though 95% of the people who hear it will still think they're special and don't need to learn their craft before jumping into cool stuff.

The thing I always remember from reading Feynman's various autobiographical essays -- he would always try to figure out something from first principles.

If you don't know the 'simple, always true' laws of what you're working with, you're going to be afloat on a sea of conjecture and fuzzy thinking.