You should avoid sweet and/or sticky foods, and acidic beverages like fizzy drinks or fruit juices.
Snacking between meals is a major problem. Each time you eat of drink, your teeth are attacked by acids for around 40 minutes, which leads to decay. Your saliva washes this acid away and re-mineralises your teeth, but it needs time to do this. If you snack frequently the acid is never washed away and your teeth become damaged.