The first thing you do, after washing your hands, is to wipe your ceramic with a damp sponge; not wet, just slightly damp.
This is to remove any loose ceramic dust - the powdery feel on the surface.  If your chosen ceramic is a vessel that will hold liquid then make sure you wipe right down to the bottom in the inside.  Any residual dust can prevent the dip glaze covering properly which could result in it not being waterproof.  It is preferable not to make the bisque very wet or each layer of paint will take much longer to dry.