The laws for skateboarding helmets vary from state to state. Many states require that skaters wear a helmet under a certain age, and some states like California make all skaters under 18 wear a CPSC Certified helmet at all times. CSPC skateboard helmets usually have an EPS protective liner that meets the safety standards for skateboarding. Make sure you check your state's regulations before ordering.
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.
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.