There are a few basic principles behind this to work. Most of them are common but most of us are just unaware about it. When we read about them and think deeper, we tend to understand it and begin to realize that such things are possible.
Take a simple example of children. Children are open to almost everything. They take whatever comes to them. Sometimes they pick up attitudes. How is this possible? If they observe somebody so something, they might pick up a certain behavior, but if we observe closely, it is just not the behavior, it is the entire attitude picked up and it lasts for days or months and sometimes years! Sometimes parents find it difficult to understand where did this come from. It is because they are affected by energies of certain individuals and these energies stay with them until cleared out. Parents and teachers do the clearing on regular basis by various methods and they also replace the cleared area with the attitude they want to plant.
Some of the principles behind such phenomenon are explained in the ezine posted here - http://ezinearticles.com/?Distant-Healing---How-Does-It-Work?&id=9036871