The first thing you can do is brush your teeth atleast 2 time's a day, which are in the morning and night.
The next thing you can do is avoid soda, soda is very bad for your teeth. The acid from soda can damage your teeth, and cause cavities.
Next avoid lemon, like soda they both contain acid which can hurt your teeth and even decay them.
Then avoid really sugary things like candy. Sugar piles up on your teeth causing cavities within time, yes we do need to consume a certain amount of sugar but candy isn't great for your teeth.
That being said, if you do the following you can prevent cavities, and any other oral problems.