There are a lot of mistakes that one can do when working out and the list is quite big and can take months if not years until a bodybuilder can achieve the proper discipline to practice this sport. It is always a good thing to know what the most common mistakes are and should be a reality in training for novices and professionals.
First of all there is a need to talk about cardio workout. Most of us know that you can not loose waith and get a great waist without cardio. The problem is that a lof of people overdo it and this has a bad effect just as with any excess in one's life. The best way to handle this situation is analyzing your workout. If you are lean but do not look lean and cardio is not doing anything you should cut all cardio workout to 50% of what you normally do for some time. If results appear then this is your problem. A lot of people fail to understand this.
Carbs are vital to your workout. Starting a diet with small quantities of carbs can lower your metabolism because this is how the body reacts to the lack of carbohydrates. If you take on this type of a diet you have to realize that carbs are important and you should take in some shakes with high carbs as they are the ones that give you energy. If you do not have energy for your heavy workout the body can only suffer!
Many individuals (when trying to loose weight) will use lighter weights. In order to achieve your goal you have to maintain the same standard of training and using lighter weights will not help you loose pounds. Keep on training hard and work on your diet and supplements rather than lowering your workout!