When you first start training arms, the basic exercises are all you really need to grow them. While barbell and dumbbell curls are enough for a novice, eventually you'll need to do more specific work to see those arms grow bigger, stronger, and better.
If you've been in the iron game for a while, you know what I mean. Advanced arm training requires breaking down the biceps into parts, targeting the short head and the long head separately. If you're unfamiliar with arm anatomy, the biceps brachii have two heads. (Hence the "bi" in biceps.) The long head is the outer part of the biceps, so when you see a photo of a back double-biceps pose, the part of the biceps you see is the long head.
Focusing on the long head will not only improve the overall look of your biceps, it will also help you add size and improve strength for other pulling movements. You can add this simple workout to your current biceps routine, or include it as a finisher on back days.
This workout is a quick, focused superset. You can either do it as prescribed or flip the order to add variety. If you want to do each exercise as standard sets, that's OK too, but keep in mind that it will take a little longer to complete.
Don't rest between exercises within the superset, but rest 45-60 seconds between supersets.
Close-grip barbell curl
This might seem weird, but to target the outer head of the biceps, you actually need to use a closer grip on barbell curls. Place your hands close together on the barbell—they don't need to touch, but your thumbs should be close, and your hands should be closer than shoulder-width apart.
As you curl the bar, focus on lifting with your pinkies. This will put a little more emphasis on the long head. Keep your elbows back, and squeeze the bar at the top like you're trying to crush it. Hold this contraction for two counts before lowering the weight. While you shouldn't be trying to break records with your chosen weight, make sure it's heavy enough to force you to work hard.
Incline dumbbell hammer curl
Use a high incline on an adjustable bench. Stick your chest out and pull your shoulders back. To target the biceps, let your arms hang and keep your elbows back as you curl. You should control the weight, not the other way around, so focus on squeezing the weights up and try not to swing.
At the top of the curl, squeeze your biceps for the same two-count you did with the first exercise. Then, lower the weights all the way back down until you can flex your triceps. Don't let momentum take over at any point.