Every minute counts when a tooth is out of its socket. Try to reimplant the tooth ASAP, provided it is clean. Avoid touching the root. If the tooth is fairly clean, with tweezers (if possible) remove obvious dirt and place tooth back into the socket. Ensure the tooth is the right way around. Bite down on a handkerchief to hold it in place until the dentist is available.
If the tooth is dirty, soak it in your own clean saliva. First, place the tooth in a clean small cup. Clean your mouth - Brush all other teeth in your mouth with water and a toothbrush. Rinse with water. Allow saliva to pool at the floor of the mouth (by stimulating salivation with salt on the tongue). After 1 minute spit into the cup, attempt to clean the root as best as possible with tweezers to remove the dirt. Do not scrub the root. The root cells need to stay alive for reimplantation to work. Try a second round of clean saliva if the tooth needs it.
Alternatively wrap the tooth in gladwrap and get to the dentist. The tooth needs to be reimplanted within 1 hour, maximum. If longer than 1 hour the root cells will be dead. See next paragraph.
If the tooth is very dirty, for example landed in contaminated mud, or the root cells have died, then gently clean the entire tooth with soap and water until the tooth is almost stripped back to a hard surface. Rinse with water and reimplant. The tooth may have a chance of fusing with the bone and staying in place. (Do not do this if you can afford an implant, as implants do not work well with fused teeth).
If the tooth will not go into place, leave the tooth out and seek alternatives to fill the gap with an artificial tooth.
If the tooth was loose before the accident, it may have gum disease. Reimplanting a diseased tooth will not work so well.
Antibiotics may be prescribed when you see your dentist. Take pain relief medication. Ibuprofen or paracetamol work well. Keep the handkerchief still over the next few hours. Once the tooth has firmed up a little, the bite pressure can be removed. Do not touch the tooth until the dentist can Xray this area.
The tooth will require root canal treatment to be successful.