Keeping your chef’s knife sharpened is essential to not only making your job in the kitchen easier, but making it safer as well. Using a dull knife, especially on something such as a tomato, forces you to apply more pressure than you would with a sharpened blade, which means knife slippage is more likely to occur. Since a sharp knife is a chef's best friend, it is important to know how to sharpen your knives.  

Sharpening your knife with a whetstone

The best way of sharpening a knife is with a whetstone, but it might take a little time and practice to get the hang of it. Once you do though, you’ll be able to keep your knives sharp while saving time and money.

With a wet paper towel underneath the whetstone (to keep the stone from sliding), place the stone on the counter top with the coarse-grit side up. With one hand, grasp the knife by the handle and hold the edge against the stone, point-first, with the cutting edge meeting the stone at about a 20-degree angle (think almost straight, slightly tilted). Use your other hand to stabilize the blade and with moderate pressure, slide the blade forward and across the whetstone. The trick is to cover the entire length of the blade while keeping the blade flush against the stone at a constant angle.  Do this about 10 times, then flip the knife over and repeat on the other side of the blade. Once finished, flip the whetstone over to the fine-grit side and repeat the process. The next step is to use a sharpening steel to hone the blade.
Honing the blade with a sharpening steel

Sharpening knives is a two-step process, because while the whetstone reshapes the cutting edge, it also leaves the edge rough an uneven. For a knife to be truly useful, we need to smooth out the roughness with something like a sharpening, or honing, steel.

With your left hand (or your right hand if you're left-handed), hold the sharpening steel point-down, with its tip resting on a cutting board — as if it were a post you were nailing into the ground.  With your other hand, hold the knife crossways against the steel with the back of the blade resting on the steel. Since you're going to be pulling the knife backward, toward you, start with most of the blade in front of the steel. Tilt the knife so that its cutting edge meets the shaft of the sharpening steel at the same angle you use on the whetstone. Maintaining this angle, gently pull the blade toward you while you simultaneously glide it downward along the shaft of the steel. Repeat this step nine more times, for a total of 10 times.  Switch to the other side of the blade and repeat on this side for 10 times. That’s it! Your knife is now ready for dicing onions or chopping parsley.