Useful goals should be (1) specific; (2) attainable (doable); and (3) forgiving (less than perfect). "Exercise more" is a great goal, but it's not specific. "Walk 5 miles every day" is specific and measurable, but is it doable if you're just starting out? "Walk 30 minutes every day" is more attainable, but what happens if you're held up at work one day and there's a thunderstorm during your walking time another day? "Walk 30 minutes, 5 days each week" is specific, doable, and forgiving. In short, a great goal!