Ok. I have a few areas that i would like to touch on, which imo will help you achieve your results:

1) Introduction
2) Biomechanics
3) Bicep form
4) Delts (Specifically the front delt)

Biceps are a common 'weak' point for many people. Their inflated ego generally results in too much weight being administered at the compromise of their form. I believe it is important to learn the bio-mechanics of each muscle prior to training.

The bicep is a muscle comprising of two heads. It is locational-origin is based on the scapuala (for the short head, and the long head is located upon the supraglenoid tubercle). The muscle travels down towards the elbow, whereby it meets the upper forearm. Thus, the aforemnetioned points show that the bicep is a muscle which travels the distance between one's shoulder and forearm. Therefore, as a result of its biological location, its natural movement is comprised of two motions:

1) Elbow flexion
2) Supination

The common dumbbell curl without forearm rotation addresses the flexion of the bicep. Whereas adding the rotating element while curling the dumbbell in a verticle plain of motion invokes the supination function of the bicep, thus increasing the working capacity of the muscle, leading to muscular hypertrophy - working more of the muscle mass of the bicep while providing a 'deeper' contraction.

Additionally, gripping the dumbbell off-center generally adds resistance to the supination function of the bicep muscle. For example (to illustrate my preceding point), when you hold your hand in the middle of the dumbbell, the two ends are balanced like a set of scales (whereby both facets are visualised at an equal distance from the surface). You get very little, if any, resistance on the supination. Furthermore, by holding the dumbbell off-center, you tip the balance of the dumbbell towards the pinky side of your hand. Your bicep must then work against resistance to accomplish the supination, thus adding in more resistance to the curl movement and increasing the efficiency of the exercise.

Additionally, in order to touch upon this point, tricep development is crucial for overall arm mass.

My final point in order to fully answer your question is concerning the deltoid, specifically the front delt. In order for your bicep to appear less 'long' in nature, a more developed front delt will 'cap' off your shoulder, since the bicep is located along the humurus.

References: (http://www.scienzemotorie.univaq.it/download/issn1592_5749_12_10_BISCARI...)

What are your stats...becuase i had the same problem and i needed to loose bf not gain muuscle nessecarily to get the cut thier

try concentration curls, at the top of each rep turn the pinky side of your hand towards the thumb side for a good sqeeze