A few from Reilly's article:
Never knock in the tying run in the ninth inning of an exhibition game. Far better to lose than go extra innings in spring training.
Always clear the inside lane for the faster runners.
Never hit the quarterback during practice.
Rookies shag balls, whether they are millionaires or not.
When a receiver drops a pass, go back to him on the next play.
Run onto the field, don't jog.