I've done some work with this too... once you wash your crystal, if it is new, you need to have it be in your energy for 30 days - don't let anyone else touch it... it needs to get to "know" your energy.
For healing you can place it over the afflicted area, or keep it in your pocket on low energy days...
My cat has been really sick off and on and he loves curling up on the crystal when he's ill. He's such a muggle cat - I can't even do Reiki on him... but he'll sleep for hours on a crystal and be just fine. Crystals draw out pain and illness. That's why they need to be washed after each use in distilled water/sea salt.