From time to time, I will offer some simple tips for runners. Things I have learned or am now learning along the way. The first tip (most important one ever) I share was given to me a few years ago at the Ridgewood Running Company. I was talking about getting a new pair of running sneakers and the guy measured me up and said ok, 10.5 and we picked out a couple based upon the way I had just run on the treadmill. He went to the back and came out with a couple pair. As I sat down to try them on, I noticed he brought out 11.5 accidentally. I casually mentioned this to him and he looked at me like I was a complete idiot and said, "You're a 10.5 so you have to run in at least an 11.5."
After an immediate conversation, he let me in on a little important piece of knowledge. When you run, your feet swell because of the force of gravity sending liquid in the body downward. The longer the run, the more swelling. It was like an epiphany. It all made sense. So, I walked out of their with a pair of size 11.5 Saucony sneakers. Since then I have not run in anything smaller.
Besides the blisters from a long run or marathon, or crazy race like Running with the Devil, I do not get blisters anymore.
So to summarize, if you aren't running in a pair of sneakers at least a size up from normal, change now!