Bad Habits that Could Ruin Your Fitness Goals

Allowing your "cheat days" to get out of hand
Although calorie and carbohydrate cycling is a valuable tool in losing body fat and keeping your metabolism high, allowing yourself too many high calorie or high carbohydrate meals can easily stop weight loss in its tracks.
Not eating enough calories
Many people make the mistake of dropping their calorie intake too low (approximately 1200 for women and 1500 for men) and then sustaining this inadequate intake for too long. Sure, you may lose weight faster at first, but if you eat too few calories for more than a few weeks you risk a damaged metabolism. One way to avoid this is to cycle low calorie and high calorie days. If you eat below 1500 calories for 5 to 7 days straight throw in an 1800-2000 calorie day or two. This signals your body its not really facing a famine.
Lifting weights that are too light
Many people lift weights thinking they're challenging their muscles adequately. In reality, if you do 12 to 15 repetitions without muscle burn or getting close to muscle failure (unable to perform a complete rep) you're not challenging your muscles enough for growth. Many women are guilty of "aerobic" weightlifting with weights that are too light. At least once a week you should lifting heavy enough to push to failure and include performing a few partial reps. These last and most difficult reps are what produces muscle stimulation for growth.
Not doing enough aerobics
How many exercise programs and products advertise "20 to 30 minutes of aerobics 3 times a week is all it takes to get in the best shape of your life!" This is even less than the government recommends and we know how trustworthy their advice is. Although this 20-30 minutes 3 times a week is enough for cardiovascular maintenance its not enough to create a large enough caloric deficit for fat loss. If you're very overweight or unfit this is a place to start. But everyone should strive for increased activity for health and weight maintenance.
Doing too much aerobics
Yes, you can do too much exercise and if preserving and building muscle mass is one of your fitness goals (it should be) doing more than 45 to 60 minutes of aerobics a day or more than five to six sessions a week can actually lead to muscle loss. Muscle loss equals a lower metabolism and less ability to burn fat. While not enough aerobic exercise is a minus, doing too much is too.