Wipe the ceramic tiles clean before beginning to paint. If the tiles are already installed, use a cleaner that is slightly abrasive to thoroughly clean off any grease or grime on them. Wipe the tiles down again to remove all traces of the cleaner.
Sand the tiles lightly with sandpaper to make the surface slightly rough. Wipe the tiles again to clean off any dust from the sanding. Dry the tiles with a clean towel or cloth so the paint is able to stick.
Paint the design on the tile with epoxy paint or oil-based paint. Use painter's tape to create straight line templates or use stencils for other shapes. If you feel comfortable with your skills, freehand the paint designs on the tiles.
Let the paint dry on the ceramic tiles for at least two days. This ensures the paint is set up and reduces the risk of it peeling or bubbling.
Brush on two layers of polyurethane to lock in the painted design. Water-based polyurethane is recommended, as it is less likely to turn yellowish over time. Allow the polyurethane to dry before applying the second coat.