Bill is right on.
Lump or briquettes, fill the ring. Fill the ring until you get use to your WSM. On a rib cook, I will not fill the ring, but I will put in enough that I'm certain that I have more than I need. The ring will be pretty full. For an overnight cook (butt), I fill the ring as full as possible.
You don't want to be under estimating the charcoal and having to reload (at least I don't).