The majority of my clients are older adults, and my answer pertains to that group. Therefore, it is not eccentric training as the other trainers have discussed.
I cue the need to control the movement both ways and gradually nudge them towards slowing down during the eccentric phase of the exercise. In order to apply this to the real world, I use the example of carrying a bag with items that can break and thus the need to be able to put them down slowly.
But my main cue is the focus on control throughout the entire movement.