From Christine Carter, Ph.D. who blogs at Raising Happiness:
"This year, pick just one resolution that research shows will make you happier:
1. Spend more time with friends
2. Everyday, find a way to give something to somebody. My favorite happiness booster is to give thanks
3. Get more sleep and exercise"
Here is a simple book on the topic that I like:
3 New Year’s Resolutions that Will Make You Happier | Greater Good