Sit down on a preacher bench and rest your elbows and upper arms comfortably on the pad. Grab a hold of the dumbbells and hold them up side by side in the vertical position. This is your starting position.
Lower one dumbbell down until your arm is almost fully extended and then raise it back up until your forearm is almost completely vertical. Then do the same with the other side. 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 use heavier dumbbells.
This is a great exercise for the biceps. The alternation makes it more challenging and therefore impacts your biceps more. This movement may cause some discomfort in your wrists if you are a complete beginner. If so, doing barbell bicep exercises is the best way of getting your wrists in shape to handle more advanced exercises such as this dumbbell movement.
Last but not least, keep in mind your goals when you do this exercise. If you are looking to put on some mass onto your biceps then go heavy; if you looking to shape and tone your biceps you should select lighter dumbbells.