If you want to get the most out of Crystal Healing it is important to set intentions when placing the stones. Set them in place with intent and ask the crystal for what you would like to get out of the healing. Each stone has a multitude of things that it can do for us, but don't ask for too many things at one time. Narrow it down to two or three goals. You don't want to over-stress the crystal by asking it to divide it's energies up to cover too many areas.
Be specific and concise with what you would like to achieve when setting an intention. This way the crystal knows what you are looking to gain. If you place a Red Garnet at the Root Chakra for example, you may ask simply ask to be more grounded or you could ask for so much more. Your intention for the Red Garnet could be to extract negative energy from the chakras, bringing it back to optimal health. You could also ask it to balance the energy field around the body while balancing the emotional and intellectual bodies. At the end you could add, "... and whatever the Garnet feels I need at this time." That way you leave it open to the gifts that stone has in store for you at this time.
Keep in mind that each crystal is different from one another and that isn't just with stone types. Two Garnets may have very different healing properties from one another. Where they were mined exactly, the growing conditions, and the mineral content all effect the metaphysical qualities of a stone. I have about 9 Garnets In my Crystal Healing toolkit. They each have their own gifts to offer.
If you would like to learn more about Crystal Healing I'll be offering a Introduction to Crystal Healing in September. It will be free to the public and will be conveniently located in Arlington Center at the Theosophical Society. Feel free to email me at info@ECMOmArts.com and I'll add you to the reminders list for this class. I promise not to add you to any other mailing list!