DIY interior painting by preparing the walls for painting using glass paper. If the surface you are going to work on is uneven from an old coat of paint, it is advisable to rub the surface down with glass paper to roughen it up, while removing any present nibs.
Remove as much sheen as possible from the surface, especially for timber or glossy surfaces. This ensures the adherence of the fresh coat of paint.
Next, wipe the sanded surface clean with a damp cloth and allow it to dry before painting.
There are various abrasive papers in the market that can be used either wet or dry. But those such as glass paper can only be used dry.
Do note that when you are using glass paper on your walls, you may want to halve it and then fold it into a third. This helps improve the grip. Alternatively, you can also use a sanding block.