The Guiding Hand
Whether it's dices, julienne cuts, or straight slices, your other hand has a key role to play. It stabilizes the food you are cutting, guides the knife, and determines the size of your cut.
Make certain that your fingers are curled inward and your thumb is tucked underneath. The side of the blade should rest against your knuckles, but NEVER the edge itself. Remember to take it slowly at first. It is all about technique. (With time, practice and confidence, your speed will increase, but you do not need to look like a TV chef.)