This is a popular exercise for the anterior deltoid. It isolates shoulder flexion.
Stand holding dumbbells lightly touching the front of your thighs and palms facing your thighs. Your elbows should be straight or slightly bend.
Engage your abs and pull your shoulder blades down and back. Keep your spine in a neutral position. Your head should be aligned with your spine.
Exhale and slowly raise one dumbbell up in front of your body until your arms are level with your shoulder. Your elbow and upper arm should rise together and lead the movement ahead of the forearm and dumbbell. Do not allow the back to arch or the wrists to bend.
Inhale and gently lower the dumbbell back to starting position.
Repeat with the other arm.