Always use a sharp knife as they can cut through the food with ease and wont slip and cut you as would a blunt knife.
If your chopping board slips while you are cutting a handy tip is to put a damp cloth underneath.
In this instructable i'll show you a method to dice an onion using a technique I call The Claw, this method shows you how to hold your food so you wont injure yourself.
I'll also show you how to roughly chop a mushroom.
Step 1: Method one - The Claw!
The Claw is a way to hold the food you are cutting and tucking the tip of your middle finger inwards so that the blade is guided with your knuckle and your ring and index finger's are holding the food, and the thumb is guiding the food towards the blade, depending on what you are cutting. This way your finger tips will not be in the way of the blade and neatly tucked away.
To hold the blade properly make sure your fingers are tightly wrapped around the handle, and the thumb and index finger near or on the blade.