What
>>112507 said.
AS SOON as you feel a hotspot developing, stop hiking, de-shoe, and put duct tape on that bitch.
Blisters form where there is rubbing and heat. Make sure your shoes are relatively snug*, flex with your feet, and are cool enough for the season. All leather boots will usually give you blisters in the summer because they have none of these qualities.
*Most people's feet will swell up 1/4 to 1/2 size while hiking.