Wash your hands with soap and water before handling raw ceramics.
This is an important first step for everyone before you touch the ceramics, whether you are painting or helping others. Any grease (which could be from food, sweets, creams, baby wipes or from children putting their fingers in their mouths) may not show when you paint but may repel the glaze when it is dip-glazed. This can leave pits in the finished surface which may not easily be rectified. This should be remembered if you touch any food or drink whilst painting.