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.
A rushed take-off might be the problem here. Steps 2-4 of this trick tip could help you out. In order to make your feet “stick” to the board, you have to do the movement fluidly. But don’t stress yourself out! You should rather start with some preliminary exercises until you feel safe while ollieing. It is also important to pull your foot up to your board’s nose in a straight manner to prevent it from spinning.
There are other types of ollies that you can do either alongside or combine with the ones listed above, like the tailgrab, indy grab, melon grab, stalefish, tweak, and dolphin nose. All of those skateboard tricks are performed more or less how they sound, but you might want to watch some videos on youtube to see a pro in action (as well as awesome cat videos).
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.