I'm particularly interested in number 6 on his list, which is something that I've often thought but not often seen aired in online RPG-related discussion:
SIX. Know the system, don’t be a dick about it. If you know a system, you are easier to GM for, because you know your character’s limitations. You can calculate the rough odds of a particular action succeeding or failing, just like in real life. You can make prompt assessments of situations and act accordingly, because you understand the rules of the world. (New players, of course, get a free pass on this one. But do make an effort to learn the rules, obviously, if you’re keen on sticking around in the hobby.)
He puts it so elegantly and succinctly that I have little else to add, except: yes, yes, a thousand times yes. Players, know the system. You don't have to know it perfectly, but know it enough. Your GM will love you for it.