If you want to build lean muscles you need to concentrate on the amount of weight you are lifting and the intensity that you are doing it. Lean muscle comes from working hard with high intensity and heavy weights. The most common mistake people make is to work out more often and increase their repetitions. This could be giving you the opposite result. Repetitions are not the answer. More weight and higher intensity is. To build lean muscle mass you need to be eating a mixture of protein, carbohydrates and low fat. The key is to mix it up and to eat several smaller meals a day rather than cutting back on what you eat and eating less but larger meals.