Increase your potassium intake. (Bananas, etc)
Potassium and water. It's all you can do really. Afterwards I find rolling the muscle and deep massage helps relieve the tightness and pain. I find a glass of water before bed helps, even though it makes me have to wake up to pee. It's worth the trade off
Eat a bannana and drink lots of water!
All of the above helps, but my grandmother taught me this other trick years ago that always seems to help -- as soon as you feel a Charlie horse, step on a cool ground (like wood floor or tile ) with bare feet. It sounds crazy but this always has worked for me in the past! I haven't experienced any white pregnant yet (knock on wood!) And I am hoping that it stays that way! Good luck!