There is no necessity to do any specific preparation for your first session, in fact it can be very useful for me to see the bowel before any intervention.
If you do want to prepare, it may be a good idea to increase fluid intake and that of fruits and vegetables for 24-48 hours prior to treatment, also to cut back on wheat, alcohol and red meat.
However, don’t put off having the colonic because you don’t feel you have prepared! During the treatment itself I will be massaging your abdomen, so try to avoid heavy meals within 2 hours of the session.
It is not necessary to have emptied the bowels, but emptying the bladder just before the treatment will make you feel more comfortable.