Limiting sugar intake is the best way to prevent tooth decay. It’s actually the frequency, not the total quantity of sugar consumption that matters the most. For example, eating a chocolate bar all at once is less harmful to the teeth than eating one bite every hour. Starchy carbohydrates and sticky foods also promote decay.
Limiting the decay causing culprits to meal time can be a good way out. Eating the dessert before the main course, will help the coarse fibrous food to cleanse the tooth surface from the sticky sweets and at the same time, the excess saliva produced to digest the food will help in cleaning the mouth better.
Think about drinks. Fruit juices (even diluted), as well as breast milk or packet milk bathe the teeth in sugar. Such drinks especially at sleeping time would allow sugar to be around the teeth for a very long time.
Fruits eaten as whole instead of extracting juice from them are much healthier. Rely less on processed, packaged foods and replace them with fresh foods whenever possible.