Begin by coating the whole surface in your chosen base emulsion color and let it dry completely. Then, draw out the area that you want to highlight using a spirit level and a water-soluble pencil (so that you can wipe off your guidelines later). Mark the shape’s outer border with strips of low-tack masking tape to ensure that you don’t paint outside of the lines. Finally, using a small roller, apply two coats of your secondary color inside the masked area; for hard-wearing spots such as skirting boards, seal with a coat of clear matt varnish.