Yo-Jimbo

I often find that my ankles need a lot of warming up. I'm interested to hear what others have to say, but will share what I do currently.
Use my hands to flex my toes several times.
Gently move the inside and outside ball of my foot in opposite directions a few times.
Rub my arch while flexing my toes. Making sure to rub the tendons in my arch.
Turn my ankle in rocking\rotating motions by grabbing my toes and rotating the foot in circles (both directions).
Shake the foot by grabbing above the ankle.
There are also various standing stretches that take the ankle through its normal range of motion now that it is warmed up a bit.
If seiza starts to hurt, switch to anza for while. When you feel like you could sit in seiza for a while again, switch back. Be nice to your body. You may need it later.