The obvious answer is to go to the gym. But still most of us won't spend three evenings a week at the gym. So for those who won't, the very minimum should be: 100 pushups, 100 situps, 80 minutes walking every day. You do get toning on your arms and chest after about five weeks of doing this. For many it will be good enough; and when you do 100 pushups you get enough strength that increasing gets easy.
For those who want to keep looking good as they age: stay off coffee, sugar, alcohol and tobacco. And of course drugs. All these things give you bad skin. Yes, sugar too: it destroys the fat layers under your skin. Don't remember exactly how it works, but there it is. Coffee contains a lot of free radicals, and there's no need to describe the effects of alcohol and tobacco, you have probably seen them.
Don't use a tanning bed before summer, it is bad for your skin.
Here's a tip: nowadays there are very good creams for giving your skin a slight tan, if you look pale. It is not a brown cream that you put on, like paint. No, it is white cream that reacts with your skin and gives you a slight tan for a couple of days. They usually contain a lot of Vitamin C and other good stuff too. Can be found at the pharmacy. For those of us who have skin that shouldn't get too much sun, they are a good alternative. Don't forget to put the cream on your neck too if you use it.
Use facial cream after the shower, or before you go to bed. It should also be used for your neck and the middle of your chest, since these two areas have the same kind of skin as your face. Use a special eye cream around the eyes and out to the sides where you get eye wrinkles; the skin around your eyes is more sensitive and needs a cream with smaller molecules. The good thing about these facial creams is that they take many months before they run out and you have to buy more. Especially if you use them right after the shower, because then they smear out easier and you don't have to use so much.
Use hand cream on the back of your hands.
Use sunglasses now that the sun is coming out. Even if it is a somewhat cloudy day you should use them, because the sun is still there above the clouds, causing you to squint lightly. When you squint you get eye wrinkles fast. Plus, sunglasses look cool.
For God's sake, stay off fat and sugar. No butter and cheese - you can easily eat bread without it. Put vegetables on the bread instead. If you eat pasta, buy pesto to put on it, not something unhealthy like cheese or ketchup. No hamburgers or pizza or the like, other than sometimes. You'll get used to eating healthily and you will find it easy after a couple of weeks - it is a difference as strong as switching from antimatter to matter.
Don't eat so much pasta. Make-up artists say that they can tell from looking at a person's skin if he has had pasta the day before. Also, it makes you fat.
French fries really, really make you fat. They are a true horror story. Don't eat them.
Stop biting your nails. If it is hard, put some tape over your mouth when you are at home. Apparently nailbiters don't bite evenly throughout the day but tend to do it during a few short periods a day, so if you can stop those periods you'll make it.
Floss. Otherwise you'll get a widening gap between your teeth when you get old. You want to be a goodlooking DJ when you are in your sixties too, don't ya? Also it helps you stay away from the dentist's chair. Nowadays you can buy those dental floss wands that hold the floss, the invention of which has more than doubled the number of people who floss regularly.