Thick, medium rare, beef lean, but not too lean, it's got to have a slight greasiness.
Slightly toasted bun so it's firm, but not crispy.
Cheddar or similar zesty cheese, not American
Ketchup
Helman's mayo, heavy
Onions, preferably Bermudas
Lettuce, preferably shredded
Pickles
That's it, the classic burger.