A tongue piercing is one of the fastest healing piercings out there - with traditional healing time being approximately 1-3 months at maximum.
Unfortunately, it's nearly impossible to keep the swelling down because you're causing trauma between two independent muscles (either side of your tongue is a muscle independent of the other side). Some people rarely avoid this problem, but it's not very common and there's usually no rhyme nor reason as to why they did not swell.
To avoid infection, simply keep your fresh piercing clean and avoid contact with anyone else's bodily fluids for the first 2-4 weeks. This includes sharing silverware and drinks!
Aftercare for a tongue piercing is relatively easy. Although some piercers still are stuck in the 80's, suggesting listerine and other chemical- and alcohol-based rinses, the best thing for it is a clear rinse of sea salt solution (mixture given below).
Also, for the following 2-7 days after your piercing, you'll want to keep your mouth chilled as much as possible (from ice water to milkshakes, anything cold is going to help with the swelling) and if you can take it for the first couple of days, an over-the-counter anti-inflammitory will also help you (such as Advil, Motrin, generic Ibuprofen, Naproxen).
Mixtures for sea salt solution are as follows:
1/4 tsp sea salt will make 1 cup of distilled water.
2 tbsp sea salt will make 1 full gallon of distilled water (to make in advance and take with you when necessary)
1/3 tsp sea salt will make an Arrowhead/Aquafina/Evian 1 pint bottle.
I am a professional body piercer.