Dumbbell Side Laterals require great care, for toughest interaction on the middle of the deltoid tilting forward is necessary at the waist.
When the weights are raised arms semilocked one quarter of the way, the pinkie knuckle should be twisted toward the ceiling. Finish the raise and hold for the count of two, at shoulder parallel (stay slightly tilted forward).
The pioneer of this movement is the immortal ‘Iron Guru’ Vince Gironda.
The famous Vince Gironda Window Bench, an incline with a hole in the center at head level was especially developed to impede cheating. Side laterals were performed on it prone or face down (in hole) and prevented torso sway.
More effective than dumbbell side laterals are all forms of cable pulley work with one arm using the same raise procedures.