Set up a preacher bench in front of the cable machine and then sit down on it. Rest your elbows and upper arms comfortably on the pad. Grab a hold of the bar no more than shoulder width apart and get ready for the initial lift. This is your starting position.
Lift the weight up until your forearms are almost completely vertical and a few inches away from your chin or neck. Then, lower the weight down but don't fully extended your arms at the bottom. You should always keep tension in your biceps. Finally, 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 increase the weight.
To do this exercise properly you first need to set up the preacher bench at the right distance. You don't want to be too close to the cable apparatus because then the cable will be rubbing up against the preacher front rest pad. On the other hand, it's also not good to be too far.
Therefore, depending on how tall you are and how long your arms are, you want begin by setting up the preacher bench about a foot away from the weight stack. Then do a few practice repetitions and gauge whether or not you should re-adjust the bench.