When it comes to covering dark-coloured walls, not all paints are created equal. Light-coloured surfaces cover easily with dark paints, but putting a light colour on top of a dark one requires priming. Primer is a paint and sealant that brings surfaces back to a neutral colour, over which it's much easier to paint. The most popular primer colours are white and grey. Use grey primer to cover an already-dark surface.
Prepare for painting by taping off the corners of the ceiling, wall plates and trim along the bottom of the wall.
Fill a paint tray with primer.
Apply primer with a paint roller. Do not spread the primer too thin. Roll the primer onto the wall until you have completed one, even coat. Use a paintbrush to apply primer to corners and near trim, where a paint roller will not easily reach.
Allow the primer to dry. If the dark colour still shows through the primer, apply a second coat.
Wait for the primer to dry before pouring the light-coloured paint into a fresh tray.
Spread the light paint over the primer with a fresh roller. Use a paintbrush to carefully paint corners and near trim. Apply one coat and allow it to dry. A light second coat may be needed to evenly cover the wall.