A first-degree (Shoden) class usually runs over a day or two, in a small group, and asks for no experience at all — only a willingness to slow down and take part.
The shape of a class
Most first classes blend a little history and theory with a good deal of hands-on practice. The teacher will explain what Reiki is and where it comes from, introduce the five principles, and show the hand positions — but the heart of the day is doing rather than listening.
The attunement
At some point the teacher gives each student an attunement (or reiju), a short, quiet ceremony traditionally understood to open the student to Reiki. It is calm and undramatic; you simply sit, often with eyes closed and hands in gassho, while the teacher works. Many people find it peaceful, and some feel very little — both are normal.
Practising together
You will practise on yourself and, usually, on one another — taking turns giving and receiving in pairs. This gentle, low-pressure practice is where the hand positions and the feel of Reiki begin to settle into your own hands.
Afterwards
You will typically leave with a manual, a certificate for the level, and often a suggested period of daily self-practice. A good teacher will also make themselves available for questions as you find your feet in the weeks that follow.
No preparation is needed beyond arriving rested and open. You stay fully clothed throughout, and nothing will be asked of you that you are not comfortable with.