The main things that most of us can do to keep ourselves healthy and free from such chronic diseases are to eat well and to exercise. These things are generally effective against things such as heart disease and diabetes. These are the things that I do, though I must admit that I do not do them as well as I should.
I do try to eat well, though I do eat too much. I eat a lot of fiber and whole grains. I do not eat much in the way of red meat or saturated fats. I eat a lot of fruit and vegetables. These are all things that make it more likely that I can avoid heart disease and diabetes.
In addition, I exercise a decent amount. I do at least 20 minutes on my elliptical machine every day. I bike many places rather than driving. This has helped me to have a good blood pressure level and decent numbers on my cholesterol and blood sugar levels.
This is essentially all that we can do to keep ourselves healthy. We must eat good diets and we must exercise a good deal.