It's hard I had pre diabetes symptoms last year and had to totally change my diet, I keep carbs low now and try to eat plenty green veg, fish and olive oil. Apparently if you can get you body fat burning instead of sugar burning it will be a lot better, but its hard.
The “keto” diet actually mimics (type 1) diabetes. You basically go into a state where the body burns fat stores.
One thing I found out is replacing ordinary starch with resistant starch. The body treats resistant starch like fibre so it doesn't add to the carb count. Apparently if you cool and reheat starchy foods like rice and pasta, you turn some of the starch to the resistant kind, and more so each time you cool and reheat. Works if you freeze stuff too - bread, mashed potatoes etc. Cornflakes are best cereal coz corn has more resistant starch.