http://www.aofas.org/footcaremd/how-to/foot-health/Pages/How-to-Keep-Your-Feet-Flexible.aspx
How to Keep Your Feet Flexible
Toe raise, toe point, toe curl: Hold each position for five seconds
and repeat 10 times.
Recommended for people with hammertoes or toe cramps.
Golf ball roll: Roll a golf ball under the ball of the foot for two minutes.
This is a great massage for the bottom of the foot and is recommended for people
with plantar fasciitis (heel pain), arch strain or foot cramps.
Towel curls: Place a small towel on the floor and curl it toward you using only your toes.
You can increase the resistance by putting a weight on the end of the towel.
Relax and repeat this exercise five times.
Recommended for people with hammertoes, toe cramps and pain in the ball of the foot.
Marble pick-up: Place 20 marbles on the floor.
Pick up one marble at a time with your toes and put it in a small bowl.
Do this exercise until you have picked up all 20 marbles.
Recommended for people with pain in the ball of the foot,
hammertoes and toe cramps.
Sand walking: Any chance you get, take off your shoes and
walk in the sand at the beach. This exercise massages your feet as well as strengthens your toes and provides good general foot conditioning.
Watch out for glass!