If you want big triceps, base your triceps training around heavy weighted dips. When you can do a dozen reps with a 100lb dumbell hanging below your waist - you'll have em! Also, "skull crushers" work very well to work the belly of the triceps muscle. Lye down on a bench and with your arms extended over top of you, lower a barbell to a point just above your eyebrows, then press upwards in a straight line to full extension. Aim for 8-12 reps. Don't forget, like any exercise, soon your body will be accusomed to the stress and muscle growth will grind to a halt. This is when you need to shake things up a bit by introducing new excercises and new repetition schemes. Never let your muscles get stale, thus you need to shock them into renewed growth with a variety of exercises - and of course - rest.
When I first started working out in the mid 80's, I focused mainly on upper body. Thus after a few years of training and with the help of good genetics, I had a huge upper body with massive pecs, delts and arms; however my thighs were underdeveloped and I looked very odd because my overall symmetry was unbalanced. I had naturally large calf muscles, thus I only needed to focus my training on my thighs. (quadraceps and hamstrings). After a few years of specialized training, focusing mainly on heavy barbell squats, I soon had the largest set of thighs in the gym. And even to this day, my thighs are now a strong point in my physique. Unfortunately wearing conventional blue jeans is out of the question. I have about 8 pairs of track pants that offer room enough to fit my legs into. So, just a heads up for you people who train upper body only. Dont forget work your lower body as well.