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.
In general an axle width should be chosen that is close to the width of the deck it will be used with. For example, a 7.75" wide deck will usually be fitted with trucks that have axles between 7.5" wide and 8.0" wide. (Standard truck axle nut size is 5/16"-24tpi UNF, and the thinner "jam" style with an optional nylon lock.) Trucks that are too wide can make doing tricks difficult and can cause the wheels to get in the way when the skateboard is being ridden. Trucks that are too small can be hard to maintain stability and can cause wheel bite to occur when turning.
Don’t get your hopes shot if it takes you a while to get this down. Once you know how to ollie, beginner skateboarders you can do any trick in the book with just a little bit of practice. Once you get this trick down while your stationary, go practice while moving around a little bit, try to hop off a couple of curbs. You’ll be skateboarding like a pro in no time. Just keep at it.
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.
Place your back foot on the edge of the tail (this is where you will apply a burst of force to the skateboard) and prepare to exert force through the foot’s ‘big-toe-mound’ area. Place your front foot behind the front bolts. Make sure the weight bearing down on your feet, as well as the weight of your body, is generally centered over the ‘middle line’ of your skateboard.
Smile and wave – Feel free to look around at all the other people at the skatepark that stood by and marveled at your new-found accomplishments (all one of them). I’m sure by this point you’ll be picking up roses that are being thrown at your feet, and taking a well-deserved bow as they begin to chant your name. Take it all in, thank the crowd for their undying affection, and then go get a snow-cone. You deserve it, champ.