The triceps make up 2/3rds of arm mass, so as many people focus on bicep development, it is more prudent to really focus on building muscle on your triceps if you want bigger arms.
You can use a rope attachment, or a straight bar on a cable machine. This exercise is great for getting the squeeze in your triceps. Standing with a shoulder width stance and your elbows fixed by your side straighten your arms and squeeze your triceps fully at the bottom of the exercise.
You must remember to keep a straight posture, otherwise risk using other muscles in the exercise other then the triceps.
A great compound exercise for the triceps, skull crushers can be performed with a heavy load. Laying on a flat bench, using an EZ bar, place the bar over your head with arms extended. Then bend your elbows and lower the bar towards your head, and back up to the starting position. This exercise can also be performed with a dumbbell in each hand.
Dumbbell Overhead Extension
In a seated position, grab a dumbbell over your head with both hands, then lower the dumbbell behind your head and back up again. This exercise is fantastic at getting a deep stretch in your triceps
Bench dips are also a fantastic compound mass builder. Taking two benches placed parallel to each other, place your heels on one bench and your hands on the other, then dip down and back up. To place even more tension on your triceps you can place plate weight on your legs.
Close Grip Bench Press
The close grip bench will enable you to place a great deal of stress on your triceps. The technique is very similar the bench press, but with your hands closer together on the bar; around 6 inches apart. The closer grip will place more emphasis on your triceps.