In the case that you didn't gave up after a hundred over tries, you'll start to develop a reaction to landing it. After a few hundred more tries, you'll feel you are getting off the ground and getting little air. And once you reach the thousandth try, you'll already be doing it whilst rolling and the next thousandth tries will be spent on clearing small cracks n obstacles and working towards ollieng up bigger obstacles n up ledges.
To get higher ollies, I would suggesting resting your back foot on the very end of the tail and the front foot in the middle of the deck to allow for more slide. Popping as hard as you can and catching your board in the groove of the nose with you ankle practically resting in the groove will level the board out in the air. after this initial movement slide you feet back to the bolts on the tail and nose to ensure a clean landing.