It's very simple:
Prepare the surface that you want to decorate by spraying or brushing over with matt varnish. Colour pencil adheres well to that. This step may not be necessary if the glaze is dull with age. We used a traditional onion motif. We drew the main elements on the lid and the front in dark blue. Then we accented the lines and drew the petals in pale blue.
Afterwards we added a few highlights in white. If the china is pure white, then you should use a different hue, for example pale grey. The gentle shading between the individual elements links them to form an overall design. Finally we would recommend varnishing the object so that it will stand up to being used.
Be brave: experiment! Try copying the design of your favourite tea service onto wooden napkin rings or candlesticks, for example. It’s very easy if you use this method: first trace it on tracing paper, shade over the underside with a soft pencil, lay it on the surface and go over the lines again. That transfers the pattern from the underside of the paper onto the surface of the object. Then you can sketch it in with colour pencils. As before, this doesn’t work well if the surface is shiny: it needs to be slightly rough.