Exercise should be fun.
If you make it fun, you will continue to do it. For instance, playing a game of 'Ultimate Frisbee' is one of the best exercises you can do.
Only increase activity gradually. In most cases it is best to increase distance or resistance no more than about 10% a week.
Start moving slowly and easily until your body is warmed up, then you can get into any strenuous exercise you desire.
Do not stretch before your body is warmed up. You may pull a muscle.
Do it at least 20 minutes a day, at least 3 days per week.
If you really want to be fit, gradually increase it up to 45 to 60 minutes a day, five or six days a week.
One rest day each week is absolutely required for the best health.
Vary your exercise each day to work your body in different ways, thus your whole body gets exercised and benefited.
Breath as slowly and deeply as you can while you exercise.
Breath in through the nose, and out through the mouth.
Blow your air out slowly, as though you were blowing out candles on a birthday cake.
Be sure to blow out all your air. It will cause you to get a better and more complete breath on the inhale.
After strenuous exercise always do a cool down routine, where you keep moving but at an easier and easier pace allowing your heartbeat to get back to normal.