Hi, Ginaanne. Welcome to the Forum.
Pre-diabetes is a wake-up call, or a yellow card if you like. Do nothing and the likelihood is that a diagnosis of diabetes will follow, so you're right - looking at your husband's diet is a good place to start. Also his weight if he's overweight.
You need to look at the amount of carbohydrate in his diet, in particular the carbs in bread, pasta, cereal, corn and other grains, starchy vegetables like potatoes, fruit other than berries, fruit juice and soft drinks, desserts, baked goods, sweets, ice cream, etc.
The key is to reduce his intake of carbs, either by cutting things out altogether or reducing portion sizes. Many of us manage our diabetes through a low-carb diet, which is considered to be less than 130g per day (for comparison a 'normal' diet is often quoted as being between 225g and 325g per day). There's no one-size-fits-all diet for diabetes as we all differ in our bodies' tolerance to carbs, so diet tends to be very personalised.
Weight loss (if needed) and exercise are also big players in reducing blood sugar levels.
Martin