You will be happy to know that this is an easy question to answer. There are no secrets to getting big, no expensive supplements or complicated training programs, just sound nutrition and effective training.
Training - Firstly you need to train in a manner which is geared towards muscle hypertrophy (muscle growth). This means training with a program that focuses on compound exercises with heavy weights and low reps. You need to choose a weight where you will be working with maximum intensity. In a rep range of 4-6 for example, if you can manage 6 reps comfortably, then you need to increase the resistance. During this time, you still need to focus on some type of cardio-vascular training. Not the traditional fat burning 1 hr long sessions, but 2-3 15 minute high intensity sessions per week. This will increase your physical conditioning, which will enable you to push harder in the gym. Make sure though that your cardio training does not interfere with the recovery needed from your weights. If you feel that the cardio is taxing your body too much and you are not recovering, reduce the number of sessions, not the intensity.
Diet - Remember what your goals are when it comes to your approach to nutrition. Mass just doesn't happen by accident, but is a result of high intensity training and sufficient eating. To increase mass, you need to eat more calories on a daily basis then your body uses for all its metabolic functions. Whilst your goal is + calories, you still need to focus on quality. Focus on lean cuts of meats, enough carbohydrates to meet your energy requirements, and don't forget the essentials fats. If after a week you have not increased in weight, slightly increase your total calorie consumption by 300-500 calories per day.
Most important, remember to consume a Hydrolyzed Whey Protein Isolate and a high Glycemic Index carbohydrate drink directly before and after training for best results.