Ceramic Bisque is very porous and absorbs the moisture out of the paint rapidly so always thin a small portion of your paint to use when applying the first couple of coats. If you do not thin the paint you can end up with ugly brush strokes.

Once the first coat or two have been applied with the thinned pain, you can apply the last couple of coats with paint that is a bit thicker.

Always remember that a few thin coats will give you a much better finish than one thick coat.

 There are many modern products on the market especially designed to get paint to stick to plastic and other stubborn surfaces.

The one I use is called ESP - Easy Surface Prep.  It will bond paint to any glossy surface - enamel, varnish, appliances, furniture, porcelain, kitchen cabinets, ceramic tiles, laminex and even glass.

It wilil not soften, remove or harm old finished, but lets the new finish hide and cover better ... especially on the edges. 

This is the only one I have ever used and it seems to work very well but I suggest you talk to the agents for any particular product that you choose and ask for technical data sheets if available. If you have great success with any particular product please let us know.