If you want to build powerful and big arms, building a big triceps is most important. Triceps size is more important that size of your biceps because triceps make about 2/3 of arms size. Also, having a strong triceps is also very important for many compound movements for bigger muscle groups like Bench Press and Military Press.  Triceps isn't one muscle, it is three-headed muscle and it is composed of three heads - long, medial, and lateral. To build bigger triceps you need to perform a workout that targets all three heads for bigger and stronger triceps. An ideal rep range for muscle hypertrophy is 8 - 12 and as your triceps becoming bigger and stronger you should put heavier weights to activate your triceps to grow more. Tip: If you triceps is lagging behind other muscles then you should work more on training your triceps and separate it from classic Chest/Triceps workout, or start a workout with triceps exercises first. It is right that chest...