First, get the diagnosis before you get too worked up about it. But, basically, it is about having portion control, and vegetables comprising half of your plate (protein and carbs each taking a quarter).
http://www.diabetes.org/food-a...-a-healthy-diet.html
Once you cross over to diabetes from prediabetes, it is always your diagnosis, even if you don't need medication. I lost weight and maintain my normal HbA1c by diet and exercise for the past 4 years, but I am still diabetic.
Jan