Slide your front foot as soon as you start jumping. Use the same movement you have been practicing to slide your foot towards the top end of the board, just as you jump off it and kick the back down. The front of your board should lift up as you slide your foot along it, with your foot hitting the top of the board at the highest point of your jump.
There is no governing body that declares any regulations on what constitutes a skateboard or the parts from which it is assembled. Historically, the skateboard has conformed both to contemporary trends and to the ever-evolving array of stunts performed by riders/users, who require a certain functionality from the board. The board shape depends largely upon its desired function. Longboards are a type of skateboard with a longer wheelbase and larger, softer wheels.
In 1978, Alan Gelfand, who was given his nickname "Ollie" by Scott Goodman, learned to perform no-handed aerials in bowls and pools using a gentle raising of the nose and scooping motion to keep the board with the feet. There are numerous references to Alan Gelfand's Ollie with most notably pictures in the 1970s skateboarding magazine "Skateboarder".
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.