How many reps do I need?
How many reps you need to do depends on your goals. As a guideline try and stay within 2 to 6 reps for strength and power, 8 to 12 reps for muscle size and 15 to 20 reps for endurance. If your goal is to build muscle then your reps range should be around 8 to 12 reps i.e. the weight should be heavy enough to allow only 8 reps, actually you should only be able to get 6 reps with great difficulty on the 6th, but you need to continue on to fight for those last 2 reps, it should be an absolute struggle to get those last two reps. That's where the muscle growth is. You always need someone there to watch over you when you are performing reps like these. On your next visit you should aim for 9 reps, then 10, 11 and 12, these reps should also be a struggle. When the time comes that you can force out 12 reps with great difficulty, it's time to up the weight.
How many sets for muscle growth?
Not counting warm ups, 1 good heavy set is enough to induce muscle growth, if done correctly to total muscular failure, however, very few people can or know how to use the 1 set principle correctly so 2 to 3 heavy sets is usually better to ensure muscle growth stimulation. Anything above 3 sets per exercise is usually a waste of time and recovery energy.
How many days a week should I workout?
You should workout 2 to 4 days a week and no more. You simply cannot fully recover and grow when you are working out 5 and six days a week. It usually takes 48 to 72 hours for a muscle group to recover from an intense weight training session. Only until after full body recovery will muscle growth happen. An every other day routine is good.
What exercises should I be doing for muscle mass?
You should be doing the heavy basic exercises like squats, dead lifts, and basic presses. These are the exercises when done correctly and safely will produce the best results for muscle mass. The "simple" isolation exercises can be added on later when you have gained a respectable amount of muscle from the basics. Don't waste your energy doing isolations if your goal is muscle mass fast.