Thanks Dogmama- I was about to pipe in RIM STRIPS... But you beat me to it.
Check yer rim strips ladies!
Some rim strips are better than others. I prefer the ritchey ones that look like bright yellow strapping tape, but velox is good too. Cheap rubber- not so good. It tends to shift.

In the shop we always check not only the tires but the rim strips. Also when changing a flat, take the old tube and find the hole/puncture. Then lace the tube around to the area it was at when it blew. That will help to find the problem. If it's on the inside of the tube chances are it's a rim strip problem. If not, look for something imbedded in the tire in the area. Or if it's a snake bite, well... It's just a snake bite. Either you took a hit and it pinched, or you didn't pump (I like to say "puff", but my mechanic mocks me ) up your tires before the ride.
And then there are the classic tube failures of a defective tube. Those are generally along the seams, and tend to be pretty big. I really don't find defective valves all that often. But sometimes the shop guys will tell you thats what it is just to get you on your way. It's just easier for them than really trying to figure it out.
Yeah, I know....
Anyway,
ALWAYS check your tires before every ride. And when I say check, I mean WITH A GUAGE. Road tires always seem "hard enough" even when they only have 85-90 psi in them.