Three things cause paint lines on your walls -- low-quality roller pads; applying too much pressure to the roller while you are painting; and allowing the roller pad to become too dry while you are painting. Paint lines are easy to remove while the paint is still wet, but if the lines in your paint have dried, you will have to sand and repaint. Sanding is the only way to remove paint lines that have already dried.
Clip a sheet of sandpaper to your hand sander. A hand sander has a flat-bottom surface to which you attach a piece of sandpaper. At both ends of the sander, on the top, are two clips under which you slide the sandpaper. It has a handle so you can easily grip it.
Sand the paint lines in a vertical motion. The hand sander is longer than it is wide. Since paint lines are generally vertical, hold the sander so the length is pointing up and down instead of side to side. If you sand side to side, you will create a wider area that will have to be repaired.
Apply a small amount of compound filler to the end of a filler knife and spread a light coat of the compound across the sanded lines. This is necessary only if you have sanded a noticeable groove in the paint. Allow it to dry completely. Depending on which product you use, drying will take anywhere from eight to 24 hours. Check the product label to find out how much time your particular compound will need to dry.
Sand the repairs until they are smooth and level with the surrounding wall area. If you do not sand the repairs properly, the rough compound repairs will show through the paintwork.
Prime all of the repairs with a primer that has been tinted the same colour as your paint, and a high-quality roller pad on a 27.5 cm (9 inch) roller. Tinted primer works well with dark colours and achieves even paint coverage. Allow the primer to dry, which can take from six to 48 hours.
Repaint the walls. Keep the roller pad wet at all times and do not apply too much pressure.
Roll paint on the wall in the shape of the letter "W." This pattern helps blend the paint and eliminate roller marks.