Sleep seems like the opposite of a calorie-burning activity, right? Wrong. According to the American Dietetic Association, people who get fewer than six hours of sleep a night eat up to 300 calories more during the day. A bad night's sleep also lowers your patience and performance levels, and makes you more stressed-out. Since dream time is when your skin repairs itself, going without can do a number on your complexion as well.

If work worries are keeping me up for more than a few nights in a row, I hightail it to a butt-kicking workout class, like cardio dance or barre. The concentration and motivation required to complete a class usually tucker me out mentally and physically. By the end of the day, I'm so drained that I get the best sleep ever, waking up refreshed and ready for the day.

Aim for at least seven hours of shut-eye every night -- no excuses.

When I'm in a bad mood, the last thing I want to do is throw on workout clothes and break a sweat. But a recent study found that besides giving your body a boost, working out has above-the-neck benefits, too. Just 20 minutes of cardio causes a rush of endorphins and other feel-good chemicals that can make you happy up to 12 hours after. That's an hour of happiness for every minute and a half that you work out -- talk about a productive way to use your time. Plus, working out instantly boosts your self-esteem (and nothing is sexier than self-confidence).

It isn't a coincidence: When the weather is better, we feel better, according to researchers (and my own internal barometer). Light that enters our eyes immediately increases levels of mood-boosting serotonin in the brain. Exposure to natural light may also help you control your waistline, says one study. Researchers have noted that those who are exposed to light between 8 a.m. and 12 p.m. have a 20 percent lower BMI than those who had similar food and exercise patterns, but less or later exposure to light.

To reap the benefits, get 20 to 30 minutes of light before noon. If you can't get outside, do what I do: I move my laptop to a sunny spot by the window to make sure my eyes are absorbing plenty of joy-giving light.