1. Basecoat the miniature white or light grey.
Warning! Painting white over dark or saturated colours in next to impossible. If you want to have parts of the model undercoated black, start with white and then apply black precisely where required.
2. Use a light grey paint to block areas that are to be white.
3. Apply a delicate wash of an ink/shade diluted with an appropriate medium
Warning! Using tap water to dilute ink will ruin your model as instead of getting delicate shades in recesses you will get dirty blobs around them.
This is partly because of a strong surface tension of most tap water variants and partly due to the fact that only the right medium produces a perfectly smooth paint which is especially visible over white background.
If you don't have the right paint medium at hand you can reduce the problem by adding a drop of mild detergent to your water pot.
4. Highlight the white areas with several thin layers of a diluted white paint.
Warning! Never use white paint undiluted. Most kinds of white are made with a pigment prone to producing small „needles” that will make the surface of your model look like sand.