Doing an explosive exercise prior to lifting fires up your CNS and gets your body physically ready to lift hard and heavy. Olympic lifting variations are often used, but here's one that almost anyone can do: the medball thruster. This exercise works great before squatting.
Make sure you drive your knees out as you squat down. Utilize the stretch reflex (the bounce you feel at the bottom of the squat) to rocket your body back into a standing position. Once you reach this standing position, continue to explode up while forcefully extending the arms.
Moderate weight or moderate sets? Use more reps per set, or use heavier weight, more sets, and fewer reps per set? God almighty, which is the optimal way to train for size?
There's an old saying that goes, "Give a man a fish and feed him for a day, but tell him about periodization, and confuse him for the rest of his life."