TO PREPARE:
1.    Use a grounding technique

2.    Centre yourself and bring yourself into the present.  Use your breath, and bring clamness and stillness to your being.

3.    Have the intention of wanting to bring healing, but do not have attachment to the outcome.

4.    Ask for healing. Ask for the highest and best for the client.  Ask your guides and angels to help you and guide you.

5.    Remind yourself that you are not the one who is doing the healing, you are merely offering yourself as a channel for healing energies.

6.   Give thanks

NOTE: It is not essential that these steps be followed.  Simply placing your hands on someone, and asking for healing is enough to allow Reiki to flow. This is the beauty of Reiki; the simplicity.
Sometimes however, students like to be given some steps to follow, until they feel confident enough to trust their own guidance.  Also, sometimes having a ritual helps to put you in the right frame of mind to maximise the energy.