Stand with your toes touching, heels far apart. Slowly raise your heels and slowly lower them.
Stand with your heels touching, toes far apart making a V shape. Same again: slowly raise and lower your heels.
Repeat each ex 10 times. I do them before and after a run but also during the day at the sink or whenever I think of it. It is ok to lightly rest your hands on a table to keep your balance