To add to sally888, avoid eating white foods; white flour, white bread, potato's, white rice, pasta, etc. These are particularly high in carbohydrates which after eating enter the blood stream as sugar. Avoid consuming sugary drinks, fruit juices and/or juices made from concentrates. Eat fruits with other foods to lessen the absorption rate of fructose [fruit sugar] into the blood stream.
To reduce your ha1c, you need to avoid foods that raise your blood sugar. in particular this would mean avoiding refined carbohydrates. The best way to see the effects of food on your sugar levels is to test using a home test kit 2 hours after eating.
If your levels are really high medications like metformin may also help.
However, if your levels are really high you should be working with a doctor to optimise your levels.