If you smoke, then quitting smoking is the most important thing you can do to protect your feet. Smoking reduces the circulation to your feet tremendously. It increases your risk of getting severe damage that might require amputation of part of your leg. You should continue to eat a healthy diet and work to keep your blood glucose as close to normal as possible.
Use common sense to protect your feet from damage. Remember, you will not be able to feel it if you step on a tack or a piece of glass, so avoid walking around barefoot, and make sure you test the temperature of bathwater before putting your feet into it. It is best to avoid using heating pads or hot water bottles. Almost all causes of foot ulcers, infections, and amputations begin as a minor injury that could have been avoided. When trimming your nails, do not cut them too close to the toe. Trim them to the shape of the toe (not straight across), and buff them with a nail file. You want to avoid leaving sharp corners or edges. Another common cause of an ulcer is when a sharp corner of nail from one toe gets pressed into the toe next to it in tight-fitting shoes.
Use lukewarm water and mild soap to wash your feet. If the feet are dry, use a moisturizing lotion on them. Check your feet every day for any signs of injury or skin breaks of blisters or hot areas or athlete's foot fungus infection. If you can't see the underside of your feet, you should use a mirror or have someone else look for you. Use socks that are loose-fitting and will wick away moisture (so cotton rather than nylon is best).
Choose shoes that are well-fitting but not too tight. They should allow enough room around your toes. If your feet are oddly shaped, you may need to see a podiatrist (a foot-care specialist) to get shoes and insoles that are custom made to protect your feet. You should expect your doctor or nurse to examine your feet at every visit. You should ask to have this done and take your shoes and socks or stockings off when you are in the doctor's office to make it easier.
If you follow all of these pieces of advice you are very likely to avoid serious problems with your feet.