Best way is to change your diet and increase the amount of exercise that you do. The combination works wonders for most people.
You'll probably know to avoid sugar, sugary drinks, cake and biscuits, chocolate and sweet snack bars etc, but many newbies think if they have a plain white sandwich, with no trimmings, not much butter, no mayonaise, chutney etc, that they are eating healthier. In fact, the white bread is just as bad as eating sugar itself. Refined starches like white bread, white rice, pasta, mashed potatoes, all raise your blood sugar levels. Switching to whole grain products such as brown rice, wholewheat pasta, real wholemeal bread (hard to find the genuine stuff) and eat smaller portions of it will make a big difference. Exercise adjusts the way food is digested and how carbs are broken down and stored. Regular daily exercise, even in small amounts helps. Also avoid some fruits like pineapples and grapes and stick to plums, apples, pears, berries etc. The sort of fruit that grows in northern europe.
Try to ensure that the amount of carbs you eat is reduced significantly and try to make sure that those you do eat are unrefined wholegrain type products. I also switch things like barley for rice sometimes. Pearl barley hardly affects your BG levels but makes a great rice substitute. Otherwise, it's brown rice. Avoid sticky white rice like the plague.