The most common materials that are good conductors of electricity are metals, but other materials, such as carbon, can also conduct electricity in certain forms. When carbon atoms are arranged in a certain structure like graphene, they can conduct electricity well, but are poor conductors in materials like diamond.
Metals are known as the best conductors due to their natural state. Metals are typically found with one or two valence electrons in their outer shells, which allow other electrons (from electricity) to transfer efficiently through the material. The best metal conductors are silver, copper and gold while the worst are titanium and mercury.