I typically have 1-2 flats/year between two bikes, my roadie running 700 x 25 Vittoria Rubinos and my commuter which uses 700 x 32 Vittoria Randonneurs in the model with puncture resistant casing. This is in the Seattle area where roads aren't in great condition and glass is encountered pretty regularly.

I'm surprised no one has mentioned wiping their tires with a gloved hand for a couple of seconds while riding after seeing glass on the road anywhere near the tire's track. This removes small pieces of glass/thorns/sharp stones that can get stuck in the tread before they work themselves through. When changing a flat I always try to locate the offending shard inside the casing and this failure mode accounts for ~95% of my flats. They used to make tire sweeps that would mount on the brake bolt that would continuously do this for you. One thing that bothers me about my commuter bike setup is that I can't wipe the rear tire due to the fenders I use, and that's part of the reason I use more robust tires on that bike.

I literally can't count how many flats this has saved me, as that's an epistemological problem, so it may just be a superstition or OCD showing, but I FEEL like this saves me at least some flats.