Stand in front of the cable apparatus and grab a hold of the straight bar with your palms facing up at shoulder-width apart. Keep your elbows tucked in close to your body. This is your starting position.
Lift the weight until your forearms are almost completely vertical and the bar is just a few inches away from your chin or neck. Then, lower the bar down but do not allow your arms to fully extend (you should always maintain 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 increase the weight.
This particular exercise is great when you're on a muscle definition cycle. It's not the best exercise if you want to build bulk. If size and mass is your goal, you should do dumbbell or barbell type biceps exercises.
The important point to note here is that this exercise requires getting into the perfect position to balance yourself properly in order to offset the pull forward that you will feel. Thus, the slight lean backwards is essential to getting into the right position when executing this movement. Therefore, take a moment and get into the right position before you start doing repetitions.