Since your triceps are made up of about 67% type II fibers (fast twitch), they grow better with heavier weights and lower reps. Lighter sets using a lot of reps just don't do much for tri's.
With that in mind, I like something I call "infinity singles" for triceps, which is a riff on rest-pause training. You start with heavy sets of around 5 reps, then work your way down to doing singles as you fatigue. You keep the single reps going until failure, which surprisingly takes a while.
Here's how it would look with single-arm rope pushdowns. Trainer Aaron White demonstrates here, but we abbreviated the set for demo purposes. In an actual workout, one set can take a couple of minutes.
- Start with a weight on the stack that you can lift about 5 times. You'll use the same weight throughout.
- Using one arm, do 5 reps. Now immediately switch the other arm and do 5 reps. Squeeze the triceps hard and hold the contraction at the bottom for a second or two. If you're not making an ugly face, you're sandbagging it.
- Without rest, go back to the first arm and do as many reps as you can. It might be 4 this time since your "rest period" only lasted as long as it took to do the other arm.
- Continue going back and forth between arms, without rest, until you can only do 1 rep with each arm.
- Here's where the infinity singles begin. What you'll notice is that you can keep doing single reps for a LONG time. That's because each arm is getting around 10 seconds of rest between each single. That's just enough time to recover and be able to do another rep.
- Stop this extended set when you just can't do another single in good form. Your triceps will feel so pumped that they almost cramp up.