Have enough experience using your hands to heal yourself before you start treating others. This is one of the first things you can do. And if you do Reiki on someone else, the hand positions would be almost identical.
You can now hear about the hand positions that are learned from Hawayo Takata's and her students' Reiki practice. You may also experiment with other hand positions taught by Mikao Usui or Hayashi. The hand configurations would most likely be similar to those found in western Reiki. Finally, you can start with some hand positions to allow your instincts to lead you. Your hands will be guided by the spirit to where they are most important.
Before you start experimenting with hand configurations, make sure you follow these instructions.
It's important to make the Reiki receiver feel at ease. Allow them to lay down on their backs on a comfortable massage table.
You should be standing or seated as the Reiki practitioner. Choose a comfortable position that will allow you to do Reiki effectively.
You should be able to step around the table without touching it.
When doing all of the Reiki poses, try to hold the fingers together.
Make gentle transitions from one role to the next.
When working on some organs or chakras, study them and learn more about them.
When doing Reiki on another human, keep all ethical issues in mind.
You may also want to read more about Reiki Healing here.