To improve the development of the upper arms, specifically the biceps, focus on lifting (supinating) the pinky side of the hand higher than the thumb side of the hand during the concentric (lifting) phase, as well as the eccentric (lowering) phase, of the movement. This would be for a greater stimulus and more recruitment of muscle fibers.
If given a choice, I would almost always select dumbbells over barbells. I am not anti-barbell, just pro optimal output. This principle of supination can still be applied when using a straight bar and/or ez curl bar simply by pushing the pinky side of the hand up through the bar. Although the hand remains in an unaltered position throughout the movement, the force being applied to the bar greatly activates and fatigues the biceps.
Always contract the working muscle as hard as possible during the movement, as the body does not know how much weight is being lifted, but how much tension is being generated. In this instance for the biceps, before even starting to bring the forearm up to the bicep, contract the triceps to make sure your fully lengthening the biceps. This is then followed by contracting or squeezing the biceps and then shortening the biceps by bringing the forearms to the biceps. This does not mean that weight isn’t important, because it is. However, it is choosing the appropriate weight for the amount of desired repetitions, while still maintaining optimal form, posture and optimal force imposed upon the muscle which will allow for the greatest development.