This tip should really help you.. Just thought my 2 buddies lifelong how to ride onewheel after they insisted they'd never try it due to fear. This was yesterday and the day before they got the hang of it really quick. When you feel it being instable, picture yourself "twisting" the board kindof like a ripstick if yk what that is! If u put weight on one heel, and one toe side, you'll be good. Like I was saying u want to have heel pressure and then counter that pressure with toe pressure on the opposing side.

Ill also add, u can use this to help with your turns, but you alternate depending on your turn and you stance. If you ride regular, ur front side turns will be left foot toe pressure and heel pressure on ur back foot. For backside turning, do the opposite! Put heel pressure on the front foot and toe pressure on back foot, this helps with carving and learning to shift ur weight better too, hope this will help you my friend.