I've always started with clears, for the various reasons cited above. I also struggle to warm up adequately for the first game of the day without fail. One of my pet peeves when I start with clears is the tendency for opponents to play very attacking clears to the back tramlines. Hardly a way to warm up, especially when you decide to respond in kind and they play a drop shot... So that said, i'm going to trial starting with drives and see how that goes!