Long snappers should employ a few things before performing a long snap:
Each long snapper should grip the ball the same- with two hands. The dominant hand is on the upper third of the ball with the other hand on the lower third of the other side of the ball. This helps the ball has a spiral when snapped. This grip also mimics that of a quarterback would grip before throwing a pass. The grip is the first step to ensure you have full control over the ball.
The player's stance is primarily the same of any hike or pass from center. The player should be bent at the knees and maintain enough balance that he isn't unsteady. The eyes should be looking to the ball and back up at the field, and arms should be long when making contact with the ball on the ground.
PRO TIP: You should be in a shuffle stance, where you can easily pivot, run forward or backward. If you feel like you'd trip before making any of those moves, readjust your positioning to be more comfortable.
The key to a successful snap is for the ball to reach the target as smoothly as possible. The ball should meet the target's hands in a straight line, since he is directly behind the snapper, regardless of the distance. But some items can throw off the snap's success.
If the players raise their hips while snapping, it can throw off the linear nature of the throw and also the snapper's balance, causing the ball to be skewed to one side. With the straight snap comes the follow through, meaning that to cover distances of 15-20 yards, there has to be enough power to get the ball there. A follow through provides an extra boost of force and power to get the ball where it needs to be.
Pretend like you're throwing your thumbs to the target. This takes the pressure off of aiming the ball to the target and helps you visualize a straight line between you and your teammate.