"Shape your environment so that it's easier for you to make behavior changes, don't just depend on willpower," he said.
Have healthy foods and snacks readily available at home and at work, so you can control what you consume. When dining out, although you can't control the restaurant, you can control what and how much you eat when you're there.
Tracking is another important component of successful weight loss, Kushner explained. "When people fall off the weight-loss wagon, it's often because they stopped tracking what they were doing and stopped weighing themselves."
Because people often feel bad about overdoing it in December, they may feel guilty when January 1 comes along and seek to aggressively change their eating habits, said Keith Ayoob, an associate professor at Albert Einstein College of Medicine in New York. "But they get too ambitious and don't realize that making permanent changes are hard."
Another common mistake he sees is that people focus on what they will eat less of and not on what they will eat more of or what is missing in their diet. Changing eating habits then feels like punishment if people are giving up their favorite foods.
This ultimately ends up in the dieter feeling deprived and resentful of a new style of eating so "all hell breaks loose."
A better approach is building in small amounts of a favorite food to keep you on track.
"Ban the concept of forbidden foods," Ayoob said. Think instead, "all foods are okay, but not all the time and not in all amounts."
Another weight loss pitfall is that people want instant results and make goals that are too general and lofty, like "I want to eat better."
Ayoob will try instead to pin the person down to a small gradual goal and suggests giving yourself simple things you can do for a month to achieve that result.
"Slow and steady wins the race" is Ayoob's philosophy for lasting lifestyle changes. For example, most people, he says, need to eat more fruits and vegetables each day. He advises patients that they don't have to get to this end point all at once, do one thing at a time. Add an extra piece of favorite fruit each day, for starters. Make sure there's at least one vegetable at dinner -- every night.
Ayoob also suggests getting organized about food shopping and chopping, and working to ensure food preparation is fun and meals involve the family.
With the holidays behind you, the new year is a great time to quit smoking, and millions of Americans will attempt to do just that.
"There's a psychological benefit to starting off a year fresh, and a little more of a commitment on people's part -- at least for the first week or two," said Dr. John Spangler, director of tobacco-intervention programs and a professor of family medicine at Wake Forest University School of Medicine in Winston-Salem, N.C.
Successful quitting entails both a motivation and a desire to break the habit.
"When I talk to patients about why they want to quit or whether they're ready to do so, I often hear comments, such as 'I want to, but I'll miss it' or that 'smoking is my best friend,'" Spangler said. "For many people, smoking has been a companion when they're bored or stressed, so quitting means ending a long-term relationship they've had their entire adult life."