Take a person that is in front of you. A person which you never knew before. And then stare at it. While starring, try to ignore how it looks his body and concentrate on the energy that his spirit gives out of the body. Maybe you won't be good at the beginning, but in time with practice, you will get better and you will be able to do it faster.
P.S: I also read that some persons can be born with this gift, but if they doesn't work with him, they will lose it in time. And if you were not born with this gift, you can get it with lot of practice.
Hope I helped you! Good luck!