Building muscle mass comes from focusing on 3 key components:
1. Eating Good, Wholesome Food
2. Working Out Hard.
3. Getting enough rest
Stick with protein sources like fish (tuna, salmon, haddock, cod), turkey, chicken, red meats (flank steak, lean ground beef), dairy products (cottage cheese, milk, low-fat yogurt), eggs, shellfish, scallops, and protein supplements (whey, egg, milk, soy protein supplements)
Your carbohydrate sources should come mostly from fruits, brown rice, whole grain breads & cereals, bagels, oatmeal, pasta, potatoes, vegetables (broccoli, green beans, corn), and legumes (chick peas, lima, kidney, and soybeans).
Finally, you also need quality fat sources like olive oil, peanuts, peanut butter, almonds, safflower oil, sunflower oil, walnuts, flax seed oil, borage oil, avacadoes, fish oils (salmon), cla (conjugated linoleic acid).
Building muscle mass is the result of overloading muscles so that they respond by getting bigger to handle that overload.
Its important you use heavy weight and low reps and sets to build muscle. High reps with low weight will do nothing for building muscle mass. Always remember, muscle needs to be forced to grow and you do that by lifting heavy with low reps.
For conditioning and toning up - more reps at a lower weight
Rest is vital. This is when your body does its repair and growing. Try to get 7-9 hrs sleep per night and a regular sleep pattern if possible.