This trick is the key to virtually every other street trick that exists; the cleaner and higher your ollie is, the easier it will be to learn everything else.
To do an ollie, I put my feet back foot on the tail, using your toes to snap it; front foot anywhere before your front bolts, depending on how high you want to ollie.
To do it, you snap your back foot back so your tail hits the floor. As soon as your tail hits the floor, bring your front foot up to the grip tape so it slides up, brings it up.
Level your back foot out with your front. Then when you're ready to land, land it.
It is easier to land an ollie moving, as opposed to being stood still. I find it easier if you find half a Silent Night bed in a carpark, to ollie over. If you don't have half a Silent Night bed, a curb will do.