Prepare the room for painting. Remove what furniture you can and protect other items with sheets and the floor with newspapers. Use masking tape to prevent paint splatters over light fixtures, skirting boards and other places where the painted walls meet another surface. Open the windows before you commence work. It is not healthy to inhale paint fumes.
Use the roller to apply a coat of white emulsion to the bulk of the walls -- and the ceiling if applicable. Finish off the edges with a paintbrush.
Tint your white emulsion a softer version of the final color if you want another bold color. For example, if you are planning purple walls, tint the paint a soft lilac and stir well. If your new color is neutral, stick with white base coats.
Paint the walls with the tinted paint after the previous coat has dried. Normally, you need to wait at least a day between coats.
Remove the masking tape when the second coat has dried. Cover any remaining scraps of yellow with a narrow paintbrush.
Apply fresh masking tape to the edges and paint the walls the final color. You may need more than one coat of this paint.
Remove the masking tape and fill in the edges as before.