Avoid sugar
Sugar is generally perceived to be the worst thing for you to eat, as it converts the mouth into acid which rots the teeth.
Beware of sugars in unexpected products such as cereals and baked beans which up your sugar count without you knowing it.
The best time to eat sugar is just after a meal as this is when you have plenty of saliva after eating. It is much more harmful to have a sweet every 20 minutes then it is to devour the whole bag in one go.