If your instinct tells you to place a green stone over the heart chakra, do. If you are reading the person's aura and see that their aura is a nice green color, but there is a yellow spot that looks imbalanced, you might want to place a blue stone there until there is a balanced green throughout the auric field. Visualization is an excellent companion to crystal healing. Visualize the aura smoothing out and vibrating with a healthy glow. Along with visualization, there is sound.
Sound creates color.
You will notice in the list above that there is a note beside each of the areas on the list. These two things, visualization and musical notes, increase the vibration of the color and strengthen the healing properties. Then just allow the stones to remain on the body for however long you feel is necessary. If the person experiences any discomfort whatsoever, any numbness, headaches, dizziness, or emotional distress, remove the stones and end the session. This applies to healing yourself as well.