Although this might seem like a no-brainer, keeping your knives clean is an essential part of proper knife use, as it kills harmful bacteria that might contaminate food.
To clean your knives, use hot water and dishwashing soap, making sure the sharp end is pointing away from your body and that you keep your fingers away from the blade. After you're done washing them, dry your knives off with paper towels or with a dish cloth. If you use a dish cloth, avoid running it down the length of the blade, which may cut the fabric (and possibly your hand).
You should also avoid leaving knives to soak in the sink for several reasons. First, prolonged exposure to water can damage the handles of knives -- especially wooden ones -- and can cause even the most expensive blades to rust. But most importantly, knives left in a sink of water can remain hidden from view, creating the risk that you might reach for something and accidentally cut yourself.