If someone you are going to help has been given a diagnosis by a doctor remember that the doctors instructions should be followed to the letter. Crystal healing is a complimentary therapy used to help regular medicine.
Start by preparing a comfortable place where they can lie down on their back if possible. It could be a bed couch or a mat on the floor. Make them comfortable and warm as they will need to be completely relaxed. Perhaps play relaxing music and make sure there is water near by if they need a drink.
When they are in a very relaxed state of mind, you can begin the process of grounding and channelling. You may open and clear the chakras and then close them again or you may place crystals around or on the body of the patient. You could choose to let the patient choose the crystals they will be drawn to the ones that they need.
One final thing about healing and that is permission. It is very important that you consider the spiritual and ethical implications if you decide to send someone healing without first getting their permission. Firstly it helps if the person actively participates in their own healing process. However it can be very disempowering to be told later that you were sent healing. It could be considered invasive of against the persons free-will however well intentioned your motives are.
Secondly every being has the right to keep their illness or imbalance. It is often necessary to go through this to find a new spirituality and equilibrium. You could be interfering in a much wider process.
If you want to distance heal and have no permission send energy for the Highest good this way the energy will be used by that person whichever way they need.