Walls are like a history book. Everything that happens in the house, remains “written” on the walls. If you have people over, for example, and most of the smoke, all that nicotine sticks on walls like glue.
Of course, you can thoroughly wash the stain out, but even if the walls are covered in washable paint, if you scrub and scrub, discoloration appears.
First thing to do, before using any kind of cleaner on the wall, is to dust it very well. Be sure to use a soft duster. Do not use a hard brush or you will end up with white marks.
If you do not own a soft duster, use whichever brush you have, and tie an old t-shirt over it or a large microfiber cloth, if you wish to clean the ceiling, for example. The areas where you can easily rich, just use a dry microfiber cloth and gently wipe by hand, without using the brush. You can also use a soft sponge.
If the wall has no stains on and you just want to wash off the dust or nicotine, just try this as cleaner: mix a teaspoon of lavender oil with 1 l of water and put the liquid in an empty spray bottle to easily use it. Spay the wall and gently wipe with a soft microfiber cloth.
To get stains off of walls, you can use a soft paste made of baking soda and water.
For crayon marks, use a cloth dampened in turpentine or apply a little toothpaste (leave to act for a few minutes, then wash off). Toothpaste can also be used to remove black marks from rubbed objects.