If a tooth is completely knocked out, it should be quickly rinsed off with water, but never scrubbed. The tooth should be held by the crown (top), not the root, so you do not damage the ligaments. In a cooperative adult, the tooth should be put back in the socket.
Many people may be uncomfortable re-implanting the tooth on their own. If this is the case, be sure to transport the tooth to the doctor or dentist in saline, milk, or saliva.
You may also place the tooth between the cheek and gum line of either the person who lost the tooth or any willing adult. The mouth is the best place for the tooth because it protects the root by keeping it moist and providing protection against bacteria.
Do not transport the tooth dry. This will cause damage within minutes. Transporting the tooth in water is also not recommended.