Stand up and hold the dumbbells down and to your side with your palms facing forward. This is your starting position.
Lift one dumbbell up until it is a few inches away from your shoulder (or until your forearm is almost vertical). Then, lower it back down to your side, but don't fully extended your arm (keep tension in your bicep). Then do the same with the other side. Repeat entire movement for the desired or prescribed number of repetitions.
Perform this exercise in a smooth and fluid motion
Don't extended your arm(s) completely when your lower the dumbbell(s)
Don't swing your arm(s) in an attempt to lift the dumbbell(s)
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or use heavier dumbbells.