Always ride the widest, lowest-pressure,
most supple tires you can. That last one might be the most significant factor (but also drives up price)
CyclingTips Podcast, Episode 9: Rethinking road bike tire sizes and pressures | CyclingTips
My Surly CrossCheck is wearing Schwalbe Hurricanes; not terribly supple perhaps (they're no Marathon Supremes), but 700x50 in the back and 700x42 in the front. I check the pressure every day by riding over the steel triangular bar that the parking lot gate at work rolls on. When they get too low, I find they're down around 15-20psi, so I air them 'up' to 30.