Hi Amy and welcome
It is good that you are taking your pre diabetes warning seriously and looking to change your diet to tackle that before it becomes full blown.
The two main options are to reduce your carb intake and/or to lose weight by a calorie restricted diet. Increased activity will also help and it doesn't have to be anything overly exertive, a good brisk daily walk is ideal if you are able.
As regards reducing carbs, this will have a direct impact on reducing your Blood Glucose levels as all carbs are broken down into glucose by the digestive system and absorbed into the blood stream. As diabetics we have become less efficient at distributing that glucose to the muscles, cells and organs of the body because either we don't produce enough insulin which enables the glucose to pass out of the blood into the cells, or perhaps due to too much fat, the cells are resistant to the insulin and don't readily accept the glucose. If we don't eat so much carbohydrate then we put less glucose into our blood stream in the first place so an excess is less likely to occur.
Carbohydrates come in a number of different forms but can be broken down into 2 main groups.... sugars and starches.
Sugars can be the granulated beet or cane sugar we put in our tea and coffee and on our cereal, but it can also be the natural sugars in fruit and fruit juice, or honey or maple syrup as well as all the things which are made with sugar like sweets and chocolate and cakes and biscuits etc.
Starchy carbs are usually derived from grains or starchy tubers like potatoes. So anything made from grains like bread, pasta, rice, couscous, pastry, breakfast cereals and potatoes, sweet potatoes, parsnips, cassava etc. Beans and lentils can also be quite high in starchy carbs.
That doesn't mean to say that you should avoid all these foods but be aware of portion size and reduce them..... so if you normally have 4 roast potatoes and 2 Yorkshire puddings with your Sunday dinner then maybe just have 2-3 roasties and one Yorkie and have more leafy/green veg on your plate instead like cabbage or broccoli or kale or cauliflower. Opt for lower carb fruits like a few berries instead of a banana or some grapes. Have some whole milk Natural Greek yoghurt with a few berries and mixed seeds for breakfast or eggs which ever way you like them instead of cereal. Swap to a seeded or low carb loaf instead of white or wholemeal bread and smaller/thinner slices or try a Ryvita style cracker instead. Have more sauce and less pasta and more curry and less rice. You can swap rice for grated cauliflower or mashed potato for mashed cauliflower. Works great with bangers or used to top a cottage/shepherd's/fish pie with plenty of grated cheese on top of course. It takes a bit of getting your head around following a low carb way of eating but it can be quite enjoyable once you get figure out what to buy and how to cook it.
The other option is to follow a low calorie diet to lose the fat which may well have developed around your liver and pancreas as well as in the cells of your body. Burning off this fat with a very low calorie short term 8-12 weeks diet can, in some cases, reverse type 2 diabetes but you need to find a sustainable way of eating after that because if you put the weight back on, then the diabetes will likely return, so if you have been a yoyo dieter in the past this may not be something which will work for you longer term.
Anyway, that it kind of it in a nutshell. The amount of carbs you opt to eat will vary from person to person and some people will need to reduce it to quite a low level for their body to cope whereas others can get away with just a slight reduction in portion size and making treats a more rare occurrence than an everyday indulgence.
We are all different with different bodies and different tastes and different gut bacteria so we all respond to specific carbs in different ways and whilst some people can get away with a bowl of porridge for breakfast, others can't or maybe don't want to. Some can manage 130g carbs a day whilst others can only cope with 40g. This is where the confusion starts to creep in and the only real way to see how your body responds is to get a BG meter and use it to measure the effect specific foods have on your system. If you are interested in doing this we can give you suggestions for reliable and economical BG meters to use and a test regime framework to help you but as you are not fully diabetic, some moderation of portion size and restriction of treats should be enough to push your levels back into the normal range. .