Hydrate better.

I used to have those regularly, crazy painful ones with my thigh muscle bulging at a seemingly impossible angle.

I started drinking a big nice mugful of light tea every evening and it has not happened again.

Also, if you’re waking up and you’ve got that feeling you need to stretch, which is how those often start for me, try curling up into a ball instead. It satisfies the need the same and I never had a cramp doing that.