To build muscle mass you should focus on a training program that involves high volume (sets/reps) using weight that is approximately 75-85% of your maximum lift capability for each exercise. You will also need to increase your calorie intake to at least 250 – 500 calories over your daily BMR. Please refer to the SHF Meal Plan system to learn how to build the perfect meal plan for your body and goals.
As you begin to train with 70-85% of your 1RM (1 Rep Max) you want to target a rep range of 8-12. The last 2-3 reps should be to the point of failure. If you are able to complete the entire set without any struggle, then you may need to increase the weight.