Tongue rings are not a piercing for the faint of heart. It takes about 2 weeks to heal completely, during which time you will experience swelling, inflammation and increased sensitivity in the pierced area. Speaking and eating will be difficult, and there are certain foods you will have to avoid.
History
Tongue piercing was a practice utilized by the ancient Aztecs and Mayans. Priests would pierce their own tongues, or just draw blood from them, in order to inflict pain upon themselves in honor of the gods. It was also used to put priests into an altered state, presumably to commune with the gods. However, the piercing was not meant to be permanent---priests would pass rough rope through the opening to increase their pain, but the hole would then be allowed to close.
Modern Usage
Nowadays, tongue rings are among the most popular piercings, second only to the earring. Barbells are the most common type of jewelry used in tongue piercing, since they cause the least discomfort to the tongue, roof of the mouth and teeth.
Infections
Before you get your tongue pierced, keep in mind that this can be a dangerous piercing. Improper piercings can cause severe inflammation, leading to speech impediments or severe infection. Swelling can cause breathing problems, because the tongue can block or restrict your airway.
Considerations
Tongue rings can press your teeth out of alignment while you sleep at night. Heavy barbells, especially, will increase the chances of this happening.
Accidentally biting down on a tongue ring can chip or crack your teeth. If your tongue ring is too far forward, and regularly touches the back of your front teeth, you can also risk rubbing the enamel off of these teeth.
What to Eat
For the first week after you get your piercing, you'll need to stick to a liquid diet. Popsicles, jello, pudding, seedless watermelon, bananas, ice cream and warm soup (not hot!) are all good ideas. To ensure you receive enough vitamins, drink lots of energy drinks that contain electrolytes (Powerade is a good one), or drinks with extra vitamins added (such as Vitamin Water).
What Not to Eat
Avoid spicy food, crunchy food such as potato chips, nuts or seeds and anything that is hard to chew. It will take you a few days to adjust to having a tongue ring anyway, during which time you don't want to accidentally crack a tooth biting down on your barbell. Spicy foods will irritate the piercing. Chips and other crunchy foods can get stuck in the piercing hole, and become infected when your tongue tries to heal around them.
Healing Time
It will usually be about 10-14 days before a tongue ring heals completely, but don't be surprised if it takes a little longer. Everyone's body heals at a different rate. Just continue to eat soft, easy-to-chew food that won't irritate your new piercing, and before long, you should have a well-healed piercing.