When training triceps, many bodybuilders forget one of the most important considerations for this muscle group: namely, all three heads must be worked.
My favorite approach is to use a different exercise for each head, hitting it with lots of weight, few sets and high intensity. This allows me to train my triceps twice a week following chest and shoulders. Keep in mind that my triceps have already been warmed up during those two previous sessions. A common mistake among bodybuilders is to spend an inordinate amount of time on triceps; in addition, they do not work all three heads adequately. I feel that anything more than 15 to 20 sets is overtraining.
To specifically hit each head, I use movements from three different positions:
(a) with the humerus or upper arm perpendicular to the torso (lying triceps extensions); (b) with the humerus extended above and aligned with the torso, (overhead triceps extensions); and (c) with the humerus pointed straight downward along the body (triceps pushdowns).
Pushdowns work the outer, knobby head, and the other two work the belly of the long head and the underlying third head.
With all three, I use very heavy weight. After my triceps are warmed up, I do only two or three sets per exercise, with a repetition range of 8-10, with one or two forced reps.
Simple and straightforward. I won't say painless, but it's the best method for maximizing triceps mass and separation in the shortest time.