Sit down on a preacher bench and rest your elbows and upper arms comfortably on the pad. Grab a hold of the barbell "hammer style" and hold it up. This is your starting position.
Lower the bar down until your arms are almost fully extended and then raise it back up until your forearms are almost completely vertical. On the way down keep in mind that you should always keep tension in your biceps.
Repeat entire movement for the desired or prescribed number of repetitions.
Perform this exercise in a smooth and fluid motion
Don't extended your arms completely on the downward portion of the movement
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or load the bar more.