I have also gotten a "borderline diabetic/prediabetic" diagnosis and after visiting a diabetic clinic (referred by PCP), they told me that you either are diabetic or are not diabetic, that there really is no such thing as borderline. Maybe your diet/exercise keeps it in check but if they are labeling you as being pre-diabetic then you are diabetic. With that being said I was given some worksheets with an outline of a diet I should follow.
Advice -
no white - meaning flour, sugar, rice, pasta. You want to use whole wheat, brown rice, etc. or at least limit the intake of the use of white.
sugar free on things you won't miss it - jello, popsicles, diet soda, etc.
eat many small meals a day vs. 3 big. Breakfast, snack, lunch, snack, dinner, snack before bed. Be sure to have a protein before bedtime to get you through the night - example 1/2 a whole wheat english muffin with peanut butter on it.
stay active - even if it's just walking.
And monitor your sugar readings so you know what is "normal" for you and what makes it go up or change drastically.