It is important to know about the crystals that you use.
The How: How to care for them. How to cleanse them. How to program them. How to recharge them. How to use them (placement: stone, jewelry, etc.).
The What: What are the attributes of the stone: overall, psychological, physical, emotional, spiritual and healing.
Do your research and select the stone or stones which seem to be best suited for your intended purpose. When purchasing stones, look at each one (size, color, shape, texture) as you may be drawn to a certain one or possibly a few.
Hold the stone and focus on it. If the stone speaks to you, you will feel the energy of the stone in your hand. This is a good sign that the crystal is for you. If you purchase stones online, you do not have the opportunity to do this. Whether purchased in person or online, ALL crystals need to be cleansed to clear the energies of any other person who has handled the stone.
After cleansing, program the crystal for your intended use for it as crystals can have multiple healing attributes.