No. 1: Walking
Why it's a winner: You can walk anywhere, anytime, either on a treadmill or with no equipment other than a good pair of shoes.
How to: Beginners should start by walking five to 10 minutes at a time, gradually moving up to at least 30 minutes per session. As you progress, lengthen the time of your walks before boosting your speed or incline.
Anyone can manage to do these. So why don't we. For most people, their personal health and longevity can be increased dramatically by exercise.