The Best Advice I Ever Received
Take the road less travelled
That was the bit of advice offered to me by a professor I worked for in undergrad, and though I was never offered this bit of advice by anyone the phrase:
To thine own self be true.
Both of these phrases have served me well in my travels and encounters; I have certainly taken the less beaten path for a professional career (Astrophysics). As for the second piece of advice, being true to myself forms the basis of my moral/honour system. For me that means being a decent, honest and upstanding individual even when there is no one around to witness any of my actions, and without the threat of punishment by some supernatural scopophiliac superintendent.