Dirt and corrosion can reduce the electrical current in a circuit, and is the cause of many problems with small appliances.
Tools & Chemicals:
Sandpaper, a file, an emery board, or steel wool are all effective tools to clean contacts and terminals. Solvents, compressed air, and some spray on lubricants are effective ways to remove debris and prevent subsequent fouling.
Be sure the appliance is unplugged before proceeding with any electrical work. Shock or death can result from working on live circuits. Depending on the surface, use which ever tool seems most appropriate. The objective is to remove the dirt or corrosion to allow the electrical current to flow uninhibited. Once the offending buildup is removed, a touch of spray lubricant or even petroleum jelly can prevent subsequent buildups.