Hi guys, I wonder if you don't mind If can you mention some good exercises specifically to focus on the long head of biceps which I'm having a hard time developing, thanks.
There are no real shaping exercises per se. But you can accentuate portions of some moves. In your case, seated dumbbell curls. Makes sure to rotate the dumbbellls out at the bottom of the movement (it'll stretch the long head)
Muskate explains the science well. Just focus on your overall arm. People often neglect triceps and just focus on biceps. Triceps are the bigger muscles in the arms anyways. With biceps I really like incorporating 21's into my training and get that pump going.