This video shows how to ollie higher on a skateboard. It has demonstrations from Melvin the Nerd, who shows proper technique to ollie. The ollie is done best when your board is pushed backward as you are jumping, then pushed forward as you are elevating. To practice while moving, jump over an upside-down skateboard. Once you can do that, try over an upside-up board until you reach consistency. Keep adding boards or moving the distances until you become better. If you're having trouble, pretend you're just jumping over without your skateboard. This video does a good job in demonstrating the techniques required for proper ollies.