Place a carpenter's level against the wall to detect which areas of paint are too high or too low.
Mark the high and low areas by circling them with a pencil and marking "H" for high or "L" for low in the center of the respective circles.
Sand the areas that are too high using a sanding buffer with a fine-grit sanding disc. Place the carpenter's level against the wall periodically until the high areas are flush with the rest of the wall.
Scoop spackling compound onto a flat trowel, then scrape the spackle-covered trowel against the low areas on the paint, keeping the trowel flush with the wall. Allow the spackled areas to dry for 2 to 3 hours.
Place the carpenter's level against the wall to see if the low areas are level. If the areas are now too high, lightly sand them level using fine-grit sandpaper. Move the sandpaper in small, circular motions.
Repaint the wall to create a level and an evenly painted wall.