Training the triceps consists of extension of the arm. The triceps pulls the forearm arm down, reversing the movement of the biceps. Another relatively small muscle, the triceps is harder to mentally isolate and be conscious of its every movement. Like biceps, it may be useful to watch your form (in a mirror, for example) while you get a feel for training this muscle. The key to triceps development is to prevent the elbows from moving as you perform the reps. Depending on the exercise and your goals, you want to choose what head of the triceps you want to develop, and focus on contracting that specific head. The way the triceps is designed may not allow you to completely isolate a certain head, as the others will work as well. However, focusing on the specific heads and performing specific exercises that target the different heads will help you build a balanced triceps muscle, as well as develop more control over the individual parts of the arm.