I was asked by Rafi of The Fitness Advisor last week for my '#1 fitness tip' for a post he was putting together, Fitness Tips From The Best. I set aside my reservations about whether I belonged in that category and offered the following:
Try not to let your passion for training unduly influence decisions about volume. Almost everyone trains too much and gets too little rest. Less is more.
On reflection I realise that this really only applies to a subsection of readers. Many people need to do more than they already are, given they are doing more or less nothing; but I like to apply the less is more principle to giving advice as well ;-)
I was therefore duly envious of Mark Sisson's entry, which was both shorter and more incisive:
Make your easy workouts longer and easier, and your hard workouts shorter and harder.
Anyway, check out the other dozen or so pieces of advice here. Worth a read.