-Floss before you brush at least once a day, after every meal is best
-Brush at least once a day-just before bed is best, after every meal is best.
-Drink only water or milk between meals. Most other drinks have a high acidity content that causes cavities, and diet drinks are just as bad. Things you add to water are acidic as well.
-If you chew gum or eat candy, make sure it is sweetened with Xylitol; it helps prevent cavities.
-Avoid sticky, chewy, sugary snacks, as they stick to your teeth and are big contributor to cavities.
-Check with a physician and see if you have acid reflux, it can be a contributor of decay.
-Too many acidic fruits too often in your diet can contribute to cavities.
-A post-floss and brush high and ACP (amorphous calcium phosphate) medicament applied to the the teeth just before bed and left on can greatly reduce cavities.
-Many medications contribute to dry mouth, which is a big contributor to tooth decay since saliva helps reduce bacteria and remineralize your teeth and prevent decay.
-See your dentist regularly for exams and teeth cleaning.
This is a good list of Do's, Don'ts, and things to check on that will go a long way to prevent cavities.