Improving your knife skills will improve your cooking and make your life easier in the kitchen. Ensuring you are holding a cooking knife the correct way is probably the biggest step you can take towards developing great knife skills as it reduces the amount of effort required to use the knife and gives greater control of the blade.
Correct - Light grip on blade with thumb and forefinger
The correct way to hold a cooking knife is to lightly grip the blade between your thumb and forefinger just in front of the bolster and then gently wrap your remaining fingers around the handle. Holding the knife this way will give you good control over the knife and will reduce the amount of effort it takes to use the knife.
Wrong - Hammer Grip
The most common error that people make when holding a cooking knife is wrap their hand around the handle and hold the knife like a hammer. Intuitively this may seem like the right way to hold a hammer but it results in less control over the blade and makes using the knife much harder work.
Wrong - Finger along spine
Another common mistake is to grip the handle with 3 fingers and a thumb whilst placing your index along the back of the knife. I honestly don't know how people can attempt to use a knife like this as it is just plain hard work and significantly reduces knife control.