Some tips that help me balance better:
1. Keep your back straighter than a regular squat
2. Give your pressing foot about 10-15 outward angle
3. Focus on pressing through your big toe
4. If you get in a groove you should be able to go straight up and down like an elevator, almost all the stress should be on the hamstrings
BTW these are a great exercise I highly recommend them to anyone who has balance trouble on regular squats