Friction blisters on the feet are the worst because it becomes so difficult to wear shoes until they heal. The shoe that caused the blister cannot be worn for one because it applies pressure right where the blister is. It can make the blister pop. So aside from awful pain, it increases the risk of infection too.
When I have a friction blister on my toe or other part of my foot, I put a bandage on it. I wear comfortable gym shoes with nice thick cotton socks. This is all I can wear until the blister has healed and scabbed over. And if the blister pops, I apply antibiotic ointment on it just to be on the safe side.