People tend to focus more on Preacher and Barbell curls and often tend to avoid adding workouts for short head of the biceps.
Pronated curls are one of the best exercises for short head and it makes your arm look leaner and bigger.
Aim for 4 sets of 12-15 reps, focus on quality over quantity!!
Watch it on YouTube: https://www.youtube.com/watch?v=TLt8-4T84k4
How to: Make your ARMS look BIGGER and defined! "Pronated Curls"