There's nothing wrong with attacking your biceps with a structure of 3 sets of 10 reps for a given biceps exercise. Multiple sets taken to 10 reps fall in the middle of the rep range (8-12) and are linked by studies to muscle growth, so you'll find nary an exercise scientist who'll disagree with that approach.
Even a science-based approach doesn't work forever, though. Sure, the muscle fibers in your biceps respond to a training stimulus like 3 sets of 10 by growing bigger and stronger…for a while. Yet if you continue with the same approach over the course of several months, this growth rate will slow down, perhaps to a crawl.
To resume growing your biceps at a faster clip, you must stimulate their fast-twitch muscle fibers—the ones that grow most significantly in response to moderate-rep training—in new ways. This can be done any number of different ways. You can add more weight, do more repetitions, add more sets, or reduce your rest periods between sets. All of these are examples of "progressive overload."
If you're not seeing gains in arm size or strength anymore, chances are good that you've become Too comfortable with your routine and are no longer challenging yourself in the gym.
The Fix For Slow Gains
Altering your rep scheme is one way to jump-start your training, because it hits the muscle fibers with a novel stimulus.
Let's say you're stuck at 105 pounds on the EZ-bar curl, a weight you can handle for 10 reps. Rather than try another set with 105 pounds, load 125 pounds onto the bar. You might be able to lift it for only 5-6 reps with good form, but don't worry; you've just applied an altogether different stimulus to your biceps with a heavier load!
Sets done for reps of fewer than 6 normally are usually better for gaining strength than size, but as you become stronger, you can take those heavier loads and work toward doing more reps, which is how you build bigger arms.
One common, proven method to building strength is a scheme called 5x5, meaning 5 sets of 5 reps. This protocol was popularized in the 1970s by the late Bill Starr, a legendary strength coach. You shouldn't use the 5x5 technique with barbell curls, however; it's more effective with multijoint exercises than single-joint exercises. Instead, we'll choose the weighted chin-up, which uses an underhand grip and stimulate the biceps tremendously.
The goal is to take a given weight and complete 5 sets of 5 reps, resting 2 minutes between sets. The best place to start in terms of load is with your 6RM—that is, a total weight (body weight plus added plates) that allows you to complete just 6 reps. Your 6RM should equal 85 percent of your 1RM.
The right load is one that lets you complete the first 2 sets of 5 reps—but not the third. (Do just 5 reps, even if you can do more.) Adjust the load accordingly if that's not the case. Over time, once you're able to complete all 5 sets for 5 reps, add 5-10 pounds to the load and start again.
Even a scheme like 5x5 can become stale over time, so there are other options to consider. Choosing a weight at which you fail at 8 or even 12 reps also offers a marginally different training stimulus. Concurrently adding a fourth set to increase the training volume allows you to vary the stimulus even more.