There's probably a good reason why ancient civilizations worshipped the sun. It provides vitamin D and stimulates the optic nerves to produce more serotonin and dopamine. In short, the sun literally keeps you happy and hardy.
Cardiovascular activity is extremely important for longevity. It also helps produce neurotransmitters, again, like serotonin and dopamine. Find a cardio activity you enjoy and engage in it for at least one hour 2-3 times a week.
Eat Fish & Eggs
They don't call it brain food for nothin'. The cholesterol in fish and eggs keeps your brain performing well. A fourth of your body's cholesterol is in your brain. Numerous studies have shown that they help prevent Alzheimer's. As an added bonus, fish and eggs also keep your heart strong and healthy. Sorry, vegans, but you can't get this anywhere but animals. Primitive civilizations believed that eating another animal would let you absorb its knowledge. I guess they were somewhat close.
You're mostly water. Drink lots of it. The purer, the better. Don't drink anything except water. Milk causes inflammation and is unnatural. Juice from the store is old and the vitamin C in it is just ascorbic acid. Freshly-made juice is the only exception, but drink it immediately. Any fruit or vegetable that has been cut will immediately begin losing its nutrients.
Acquire some talents. We are human. This is what separates us from primates. Find something you're interested in and get good at it. Drawing, blacksmithing, gaming, sports, whatever. Share them with your neighbor. Your quality of life will improve.
Limit Phone, Computer, and Television Use
I'm just as guilty of this as anyone else. Even if you're watching educational television, studies have shown that it still deteriorates your brain because you are not using your imagination. Spend more time each day outside of your devices, unless it is thought-provoking and productive. Do not cheat yourself with this exception.
This one is simple. Don't eat garbage. If your grandmother didn't have it, don't eat it. It's okay to cheat sometimes on weekends, but you should eat lots of simple foods throughout the week. For me, that means oats, rice, beans, whey, carrots, etc. It may not taste very good, but your increased quality of life, performance, and overall functioning will be worth it.
Old people who go to church and have friends live longer. Being lonely is as bad as being a casual smoker - oh yeah, and cut that out too if you are one. No offense!
Exercise your Brain
If you don't use it, you lose it. This seems to always be true in life. Strive to regularly partake in brain-teasers and thought-provoking activities for the rest of your life.