one thing that can really help is making sure you don't point your toes as you're sleeping. lots of people who sleep either on their back or their stomach will naturally have their toes pointed, and it causes your plantar flexors (the muscles in the bottom of your feet) to be tightened up as you sleep all night. when you wake up in the morning and start walking around, stretching out the muscles that have been cramped up all night, it can cause irritation and soreness (as if you're now hyperextending these muscles).
when you sleep, try to do so on your side, or contiously prevent your toes from pointing down and moving your feet into a plantar flexed position. you could also tape them in a dorsi flexed position (foot at a right angle to your shin), helping prevent the plantar flexors from being contracted all night.