As a rough guide try not to pick anything that says more than about 10grams per 100grams. Some people will recommend a bit lower (5) and others a bit higher (15). Make sure you read the number for the "Total carbohydrate" and not just the "of which sugars" as its the Total Carbohydrate that matters. You get the value of the back of most packets. Its usually on the label in very small writing!