The key to increasing the size of your chest muscles is to eat more and get stronger. Build a foundation before you even think of adding isolation exercises.
Eat More. Your chest will never be big if you’re underweight. Check the minimum weights for your height. To gain weight: eat every 3 hours and focus on calorie dense foods
Do Heavy Compounds. Free weight compound exercises like the Squat, Deadlift, Bench Press and Overhead Press are the fastest way to build overall strength & bulk. Do them often & heavy.
Train Your Legs. Squats & Deadlifts help chest growth by increasing the release of muscle building hormones like Testosterone and Growth Hormone. Get stronger at them. Read 5 reasons to train your legs.
Rest. Your muscles grow when they rest, not when you train them. Train your chest maximum 2x/week. Eat your calories so your chest gets the nutrients it needs to recover and grow bigger.
Lift Fast. Lifting fast recruits more muscle fibers and lets you use more weight, which stimulates chest growth. Lift as fast as you can on the way up with good technique. Way down under control but not slow.
Use Proper Technique. A partial bench press doesn’t work your chest through a full range of motion. Touch your shirt on the way down, lock your elbows at the top. Lower the weight if you have to.
Set Realistic Goals. Even if you train and eat exactly like your idol, you’ll never get the same muscle shape. Developing your muscles is training and diet. But the shape of your muscles is genetics.
Be Patient. Especially if you’re still a teen. Your body is still developing. You won’t get the chest development of a 30y old if you’re only 15. Build the foundation and be patient. Your chest will change as you get older.