Sit down on a preacher bench and rest your elbow comfortably on the pad. Grab a hold of the dumbbell and hold it up vertically. This is your starting position.
Lower the dumbbell down until your arm is almost fully extended and then raise it back up until your forearm is almost completely vertical. Repeat entire movement for the desired or prescribed number of repetitions and then switch and do the same with the other arm.
Perform this exercise in a smooth and fluid motion
Don't extended your arm completely on the downward portion of the movement; it's important to keep your bicep constantly tensed to achieve maximum impact and effectiveness
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or use a heavier dumbbell.