Sit down on a flat or military bench and grab a hold of the dumbbell "hammer" style with your arm extended and down at your side. This is your starting position.
While keeping the upper portion of your arm (from your elbow to shoulder) tight up against your body and fixed, raise the dumbbell all the way up and then lower it back down but don't extend your arm all the way. You should always keep tension in your bicep for maximum effectiveness.
Repeat entire movement for the desired or prescribed number of repetitions and then switch and do the exercise with your other arm.
Perform this exercise in a smooth and fluid motion
Don't extended your arms completely on the downward portion of the movement
Don't swing your arm in an attempt to lift the dumbbell easier; this is cheating and does nothing for your biceps
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or use a heavier dumbbell.