I have the same problem dude....I did a bunch of research and found this sick routine. Certain exercises only target certain parts of the muscle. I learnt that there are 3 major parts of every muscle...for instance in your bicep you have Fast-twitch white muscle fibres', Intermediate muscle fibres', and Slow-twitch, red muscle fibers. That basically makes up each on every muscle in your body. I have found in order to build a more full muscle you must train all parts a quick and simple bicep routine is:
Barbell curls (shoulder wide grip) 3 sets 6 reps (fast-twitch white muscle fibers)
6th rep should be extremely hard or muscle failure with fast explosive reps
Dumbbell curls (seated) 2 sets 10 reps (intermediate muscle fibers)
EZ-barbell curls (narrow grip) 1 set 20 reps (slow-twitch red muscle fibers)
Hope it helps....try it out and do more research on the different parts of your muscle and what they do....In all our cases Knowledge literally is more power!
Stay safe
-Heavy Arms