Hiya there!
Here are some good ways to prevent tooth decay and cavities:
#1 Brush your teeth regularly (at least twice everyday)
#2 Eat healthy, un-sugary snacks
#3 Floss daily (cavities tend to be caused by not flossing)
#4 Get a monthly/quarterly check up with your dentist
These are just a FEW things you can do to keep those teeth white!
Hope this helps you!
~DL