The number of times a day you eat sugar has a major influence on your chances of getting tooth decay. The simple fact is, if you can limit sugary snacks and drinks, especially between meals, you will greatly reduce the chances of getting tooth decay.
Sugar is in so much food these days - especially processed foods - you may be getting sugar unwittingly. Sugar is even in baked beans!
Sticky sugary snacks are the worst offenders but fizzy drinks cause lots of problems too. Fizzy drinks are amongst the worst offenders because - not only do they contain lots of sugar - a single can typically contains 8 teaspoons of sugar - but they also have acid in them which dissolves your teeth away more quickly.