If you fracture a tooth, rinse your mouth with warm water and use an ice pack or cold compress to reduce any swelling. Take ibuprofen, not aspirin, for pain (unless you're asthmatic, pregnant or are sensitive to it).
Minor fractures and chips can be smoothed out by your dentist, while larger ones may need a restoration, such as a filling, crown or inlay.
If you wear dentures and a tooth breaks or chips, wear your spare dentures until you can visit your dentist. If you do not have a spare set or cannot see your dentist in the near future, use cyanoacrylate (heavy-duty, quick-drying "super" glue) to glue the tooth or the piece of the tooth back into place. Make sure it's completely dry before re-inserting.
Remember—this is only a temporary measure until your dentist can properly repair your tooth and should only be used for dentures! Never attempt to glue a natural tooth or part of a natural tooth back into place.