One foot on the tail, (by foot I mean the ball of the foot which is just behind the big toe) the other foot is about an inch behind the bolts(screws) for the front truck. Basically, the back foot quickly pushes the tail down, and right when the tail of the board strikes the ground, the back foot jumps up… the tail of the board will follow up with the foot when the front foot slides forward slightly, which pivots the tail of the board upwards. Since the front truck comes off the ground first, getting the back truck up is the trick.
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.