1. Not doing the math
When it comes to counting calories, there's no eyeballing those mashed potatoes for a rough estimate. A reliable calorie calculator will tell you how many calories you are allowed per day based on age, gender, height and level of physical activity. Learning about portions and investing in a food scale can help you make more accurate measurements of how much you should be eating each day.

2. Looking to fad diets
Celebrities are quick to promote methods they employ to lose weight. Often, these diets involve liquid intake for weeks at a time and are not a practical consideration for a permanent lifestyle change, as they can lead to malnutrition and organ failure. Do they yield short-term results? Sure. Even Gandhi would lose weight drinking sugar water!

3. Setting unrealistic expectations
Because every metabolism is different, two people can eat the same amount of food, yet lose weight at different rates. While setting a goal of losing 20 pounds in one month might be plausible, it might not be possible. As long as you hold steady to your weight-loss program, it's best to avoid the "numbers" game. If you must keep track, it's healthy to judge your weight loss with inches lost or simply how your clothing fits.

4. Scale-gazing
It's a good idea to document weight loss, but scale hopping is another way to get caught in the numbers game. The scale will give you good news in the morning when your stomach is empty but level a blow in the evening when you've just had a meal. The most important thing to ask is, Do I like what I see when I look in the mirror?

5. Not limiting alcohol consumption
Whoever invented the term empty calories had to be referring to beer: One 12-ounce serving contains anywhere from 140 to 210 calories. Also, the sugars in alcohol break down into carbohydrates that are difficult for the body process, which is why you see them lingering around the waist. Cocktails can be major calorie-busters, particularly those creamy, frozen poolside concoctions like pina coladas. Stick with low-calorie mixers and one type of alcohol for a reasonably low-calorie cocktail.

6. Not exercising
Weight loss can be quickly aided along with exercise. But don't choose an activity that you abhor, or you won't stick with it. If walking on a treadmill is chore rather than challenge, pick an activity that piques your interest, such as yoga, martial arts or ballroom dancing. Grab a DVD that looks fun, if you prefer to work out at home. Not only will you lose weight, you'll learn a new skill.

7. Ignoring an undiagnosed medical condition
Sometimes the most dedicated dieter won't notice a change in weight after devotion to healthy eating habits and exercise. If you can't lose weight, it's wise to consult with a medical professional. Disorders that affect the thyroid, such as Hashimoto's Disease and Graves' Disease, can make it difficult to lose weight without treatment of the condition itself.

8. Not setting boundaries
Friends and family love you no matter how you look, and that's a blessing. Mom's not intentionally trying to sabotage your efforts when she "supersizes" the calorie-laden pasta dish you loved as a child. But it's often difficult for loved ones to recognize their enabling behaviors unless you point them out tactfully. Let the people close to you know that you've made a lifestyle change, and ask for their cooperation and support.

9. Acquiring unsafe habits
The worst case of self-sabotage is when a frustrated dieter resorts to drastic measures. The use of laxatives, self-induced vomiting (purging), and frank starvation (anorexia) are signs that you need to seek the help of a doctor or mental health professional.

10. Changing your daily routine -- without changing your mind
Inconsistent eating and exercise patterns are signs that the most important tool to weight loss has not been acquired: A change in attitude. Losing weight and keeping it off isn't just about adding up calories and putting in hours at the gym; it's about making a decision to change your way of life. It really is that simple!