Generally, sea salt and freshly ground black pepper only. If I am grilling, I will oil the grill but not the steak. If I am using cast iron, I won't use oil at all - most oils burn too quickly.
Occasionally, I will make a rub out of freshly ground ancho chili powder, ground espresso, salt, pepper and garlic powder, but I usually just keep it simple.
Never sugar or garlic - it burns right away.