To increase suspense in a scene where a dangerous person is about to do something nasty, slow down the pace and describe their hands. This is perfect for when the evil overlord signs the order to exterminate the children, or when the torturer readies his instruments.
This technique works especially well in thrillers. Show the killer’s (or the suspect’s) hands, especially when the point-of-view character is helpless to do anything. This will send creepy shivers across the reader’s skin.