Here is the answer, proper nutrition and regular exercise, period. This is the key to a long and healthy existence. Exercise for 30-60 minutes, 5 times a week. Do a mix of cardiovascular exercise and resistive exercise. If you can manage, try exercising first thing in the morning, on an empty stomach. It will rev up your metabolism and help you burn more calories throughout the day.
As for proper nutrition, start by eating breakfast within two hours of rising. Yes, it truly is the most important meal of the day. It wakes up your metabolism. If you view your metabolism like a fireplace, you've got to throw a log in to fuel the fire. Once the fire is burning, what happens in about 3-4 hours? You got embers right? This is like your body. You have to throw another log in to keep the fire burning. Think of nutrition in a different light. Eat to live, do not live to eat. Nutrient dense food is what you body needs to run at its best. In addition to eating something healthy every 3-4 hours, you must choose the foods that give your body the biggest bang.
Cut out all the whites stuff for starters. If the package states the flour is bleached, don't eat it. Eat your whole grain breads, cereals and crackers. Cakes and cookies should be avoided as a general rule. Stick to fresh fruit and yogurt with some healthy granola. Eat plenty of healthy, lean protein. Red meat is ok in moderation. Nuts are a wonder source of protein for snacking. There are healthy fats in nuts. It's ok to have a small handful, just don't go over board. Moderation is the key to your success.
Finally, water, water, water. This is essential to your health. Drink at least 64 ounces every day. Your organs will do their jobs much better if you are hydrated. Water helps your body flush out toxins that build up in the body. Hydration is also necessary to a healthy digestive tract. If you struggle with this, try using a clear 32 ounce safe sport bottle. Drink 2 daily. The first to be consumed by noon each day and the second prior to the end of your work day. Drink when you are not thirsty. If you feel thirst, you are already becoming dehydrated. Drink in the winter...the air is very dry and lends itself to your body losing vital water.
I know this is a lot to digest. Try picking a couple habits at at time to work on. Set small attainable goals. Give yourself some time to develop new habits. It typically takes 3 weeks to a month to form a new habit or break yourself of an old, less beneficial habit. You can do this, one step at a time.