Tongue piercing usually take between 10-14 days to fully heal, it is almost impossible to develop an infection because the mouth contains an enzyme "Ptyalin" and Lingual antimicrobial Peptide (LAP) which kills bacteria. Overuse of mouthwash destroys these which can cause the tongue to go green or brown, if this happens reduce the amount of mouthwash you use.
You will experience swelling the first day you get the piercing, but the worst swelling will be from 2-5 days after the piercing, during which time your tongue will be very uncoordinated and you may find it very hard to talk. The only food you will be able to eat during the first 3-5 days are things like mashed potatoes, canned spaghetti mashed up etc. or fruit and milk drinks made in a blender.
During the healing process you may experience one or several of the following problems, don't be alarmed they will all stop once the piercing is healed. Your salivary glands will overproduce saliva and this will cause you to constantly swallow, this may last for up to 5 days during which the salivary glands (under the chin) can become swollen. The tastebuds on the end of your tongue may become tender and you might experience a tingling or burning sensation. You may experience tenderness where the balls on the barbell make a depression on the palate of your mouth and on the lower inside gum of your mouth. You may see a white fluid being excreted by the wound, don't be alarmed is just dead white blood cells it's a normal part of the healing process, all wounds heal by secreting plasma which forms a scab, but because of the saliva in the mouth a scab can't form.
After 3-5 days the swelling will start to reduce, and between 7-10 days after the piercing you will have to insert the shorter barbell inserted, I can do it for you or you can do it yourself. Usually the shorter barbell can be inserted after 8-10 days, although some people's tongue may heal quicker. The amount of swelling depends on how long your tongue is (longer tongues swell more), where the piercing is placed (the further back from the tip, the more swelling) and how well you follow the aftercare instructions.