Tip #7

Here are a few pointers for those you who wish to increase muscle mass.

1. Compound Movements: Compound exercises are highly effective and efficient exercises. Such exercises include squats, deadlifts and benchpress. Squats and deadlifts are especially effective as they increase your body's production of growth hormones, in turn the rest of your muscle groups are more responsive. In other words with these exercises your body gets a greater pump, and allows you to build muscle at the highest rate possible. 
2. Free weights: While machines allow for better form with exercises, free weight exercises stabilize the muscles you don't use on a machine as there is a greater involvement of muscle fibers and muscle contractions. For example lifting heavy dumbbell weights only 4-8 reps stuns your muscles and nervous system putting them under enormous pressure. As a result muscle fibers are stimulated and encourages muscle growth.
3. Work with the weak: Your body is an entire unit, and every aspect should be worked on and improved. When one aspect is neglected, the entire unit is affected. Therefore you shouldn't concentrate only on those exercises that work only the aesthetically pleasing muscle groups, such as the chest or the biceps. Ignoring some muscle groups and concentrating on others can lead to severe muscular imbalances that can take months even longer to correct. Your body's structure actually warns against such neglect with protective mechanisms that prevent the building up of one muscle group to proportions beyond that of others. For example have you ever like me hit a wall with a certain muscle group such as bench press and you simply cant increase your weight. You may actually need to work more on those back muscles which I neglected which will allow your chest to grow more. 
4. Diet: Your diet is a major factor in increasing muscle mass. Without a proper amount of food and the right food, those hours your putting in at the gym will help your strength, however you are unlikely to get too much bigger and never reach your full potential. You need the correct balance of proteins, carbs and fats through a caloric surplus ( absorbing more calories than your body uses). This will allow your damaged muscle tissue through extensive workouts to be repaired building bigger muscles. You can refer to Salma's posts for ideas of diets. 

Goodluck and stick to it guys.