1. Refrain from eating meat, fowl or fish for three days prior to the attunement.  These foods often contain drugs in the form of penicllin and female hormones, and toxins in the form of pesticides and heavy metals, that make your system sluggish and throw it out of balance.
2. Consider a water or juice fast for one to three days especially if you already are a vegetarian or hve experience with fasting.
3. minimize your use of coffee and caffeine drinks or stop completely.  They create imbalances in the nervous and endocrine systems.  Use no caffeine drinks on the day of the attunement.
4. Use no alcohol for at least three days prior to the attunement.
5. minimize or stop using sweets.  Eat no chocolate.
6. If you smoke, cut back, and smoke as little as possible on the day of the attunement.
7. Meditate for half an hour each day for at least a week using a style you know or simply spend this time in silence.
8. Reduce or eliminate time watching TV, listening to the radio, and reading newspapers.
9. Go for quiet walks, spend time with nature, and get moderate exercise.
10. Give more attention to the subtle impressions and sensations within and around you; contemplate their meaning.
    
11. Release all anger, fear, jealousy, hate, worry, etc. up to the light.  Create a sacred space within and around you.
12. A Reiki attunement is an initiation into a sacred metaphysical order that has been present on Earth for thousands of years.  By receiving an attunement you will become part of a group of people who are using Reiki to heal themselves and each other, and who are working together to heal the earth.  By becoming part of this group, you will also be receiving help from the Reiki guides and other spiritual beings who are working toward these goals.
    

A Cleansing Process
(as per 'Reiki, The Healing Touch', First and Second degree manual, by William Lee Rand)

A Reiki Attunement can start a cleansing process that affects the physical body as well as the mind and emotions. Toxins that have been stored in the body may be released along with feelings and thought patterns that are no longer useful. This does not always take place after a Reiki attunement, but when it does, it is important to understand what is happening so you can support its completion.  Whenever changes takes place, even if it is good, a period of adjustment is necessary so that the body and various parts of your life can get used to the healthy new conditions.  You may need more rest, and it can also be helpful to spend more time quietly contemplating your  life and any changes you might need to make to support a healthier lifestyle.  Many have found that a process of purification prior to and after the attunement improves the benefit one receives.