I'd eat a light breakfast to start with.
Go for an appetizer plate first, and then go for 2 or 3 heaping dinner plates worth of food depending on how hungry you are. Don't eat a lot of bread... that's a suckers move to get you filled up quickly. Make sure to make multiple trips to the seafood section and the carving stations, because that's where all the "good stuff" usually is! Don't let them off easy with those cheap to make chicken dishes... Go for the bacon wrapped shrimp and the prime rib, big man! Make sure to drink a diet Coke with all this, because it helps to ease the guilt and almost makes this feast seem healthy!
I'd recommend the cheesecake rather than ice cream for dessert, since the "ice cream" at a buffet is usually just frozen yogurt.
Make sure to plan two hours for nap time after eating all of this, since you certainly won't feel like going back to work afterword.
Anyway... That's how the "pros" do it, man. Eat like that twice a week, and you'll be ready for a second career in sumo wrestling in no time!