It takes most everyone a long time to do an ollie but once you have it done it happens all the time. When first starting out it is a good idea to learn the technique in the grass or on some carpet so the board doesn't roll around. It's also a good idea to fully learn the ollie in place before you start doing it in motion. Next is foot placement, have your front foot right behind the front bolts on your skateboard and you back foot on the tail. When you press the back foot into the ground lift the front foot up and jump into the air. As you are in the air throw your front foot forward making the board flat out. Land evenly with both feet on the board. It is alright to fall when learning this trick just keep trying it until you've got it then try it moving.