Shiny surfaces are tricky to paint. The reason? The surface is shiny because it is super smooth and anything you put over it won't have many microscopic nooks and crannies on which to hold. So unless you are placing a tree frog on your wall, you will need to either dull the surface with sandpaper or use a special high-adhesion primer.
To dull the surface, use a fine-grit sandpaper and sand the entire surface to remove the sheen. You do not need to remove the paint layer, just rough up the surface until the shine goes away. This will give the new paint plenty of little holds in order to stick well.
But if you are like me, you won't want to sand your walls. Most people don't want to spend their time doing this laborious task and who can blame them. Thankfully there are primers you can use that will stick to glossy surfaces. These primers enable you to then use your regular paint for your final one or two coats of paint. We still recommend lightly sanding the surface before priming, but it is more of a precaution than a necessity if you are using the right primer.
Make sure your wall is clean a dry before applying the primer. One coat should suffice and then you are ready to paint.
These same high-adhesion primers will also work when painting other shiny surfaces such as cabinets, formica and tile. Just keep in mind that painting an extremely hard and shiny tile is not the best thing to do, but if you are looking for a relatively short-term solution, then these primers make this kind of project possible and even hold up fairly well.
We recommend using the 100-percent acrylic Benjamin Moore Primer. It is an excellent primer to use over any surface, and works incredibly well when priming any hard or glossy surface.