Have a happy New Year. It's a well-intentioned cliché you probably found yourself batting back and forth this past holiday season. But think about it for a minute: Deep down, do you believe you can create—and sustain—joy in a consistent way? Or does such a positive emotional state seem mostly beyond your control?

If you lean toward the former, you'll be happy to hear that recent research backs your optimism. Sonja Lyubomirsky, PhD, a professor at the University of California, Riverside, and author of Sustainable Happiness, to be published by Penguin this year, has been busily testing out what she calls happiness interventions. By and large, she says, these simple exercises are working—that is, increasing subjects' feelings of well-being weeks and even months later. The key to making your contentment last is practice, according to Lyubomirsky. So start now, keep rehearsing, and you just may ground that happy new year wish in reality.

1. Commit acts of kindness
Let that car merge in front of you in traffic. Go grocery shopping for a neighbor who just had a baby. Help your friend's kid with homework.

Why it works: Acts of kindness and generosity help foster a positive, cooperative view of your world and the people in it, and raise awareness of your own good fortune, says Lyubomirsky. Acting kindly tends to make you feel more confident and in control. (Yes, I can change things for the better!) And, not surprisingly, behaving generously tends to win more friends (remember the saying about catching flies with honey?), and friends are a great resource during times of stress and need.

Tips: To experience the greatest impact, plan out five things to do on any given day. "These are extra things, beyond ways you normally behave," Lyubomirsky says.

2. Count your blessings
For this simple daily gratitude exercise, think about three things that went well and why. If you had a fun outing with a friend, for example, credit yourself with coming up with the idea, following through on planning, and nurturing yourself by keeping close relationships strong.

Why it works: Stopping to recognize and honor the good in your daily life—and then noting your part in it—is critical, says M.J. Ryan, author of This Year I Will (Broadway, 2007), "because when people feel down, it's largely because they feel they don't have control in their lives." Ninety-four percent of people (including those who rated themselves as seriously depressed) who wrote down three blessings daily for two weeks reported a decrease in depression—some by more than 50 percent—according to Martin E.P. Seligman, PhD, author of Learned Optimism (Vintage, 2006).

Tips: Seligman recommends journaling three ways in which you feel blessed at the end of each day. If that seems too much, try journaling five blessings every Sunday evening.

3. Write a gratitude letter
Who has made a big difference in your life—a high school teacher, coach, great-aunt, first boss? If you've never thanked them properly, express your appreciation in writing, in detail.

Why it works: Gratitude promotes savoring the best of life, says Lyubomirsky. In fact, she adds, the practice of expressing gratitude appears to be incompatible with negative emotions—and thus may help lessen feelings of envy, anger, or greed.

Tips: Try writing a letter once a week; you don't have to mail it to experience benefits. However, "mailing the letter (or reading it over the phone) can have a powerful effect," says Lyubomirsky. Some of her students have found themselves crying and have experienced more intimacy and stronger relationships.

4. See the future
Envision your life ten years from now. What is the best possible future self you can imagine? Journal all the exciting details.

Why it works: "It makes you think about what you want in life," says Lyubomirsky. "Plus, just thinking about the best possible outcome makes you feel happier." Students who've done this sometimes report afterward that they hadn't realized their goals were attainable. Once you better understand what your goals are, you might find yourself taking steps toward them, Lyubomirsky says.

Tips: Write in the present tense; it will empower your vision.

5. Cultivate your relationships
When you're frustrated with a loved one, make it a practice to focus on what you appreciate about him or her.

Why it works: In numerous surveys, including a 2002 study conducted by Seligman at the University of Illinois, the most relevant qualities shared by the very happiest students were strong ties to friends and family, and a commitment to spending time with them.

Tips: This simple practice takes a mere moment. "We're always told we need to work on our relationships," Ryan says. "Here's something to do that doesn't take work."

6. Find the silver lining
Inevitably, difficulties and frustrations arise. You might have negative emotions the next time you're stuck in a traffic jam or don't get the promotion at work. That's OK, says Ryan. But afterward, ask yourself, "What's right about this situation?"

Why it works: As soon as you ask this question, says Ryan, you open the positive part of your brain. You create a way to think more creatively about the situation.

Tips: If you're stuck on the subway, for instance, you might think, "This is an opportunity to practice patience, something that's challenging for me." Missing out on a promotion might be the impetus you need to start looking for a better job or to spend more time with your family.