Start with a mild mixture. Expect a relatively small amount of vinegar mixed with warm water to be sufficient for the job a lot of the time. Simply combine 2 to 3 tablespoons of white distilled vinegar with 1 gallon (3.8 L) of water in a bucket or similar container. However: Keep in mind that you’ll be carrying that bucket around the room with you.
Depending on the size of your bucket, adjust the amounts as needed to keep it only halfway filled to avoid spills. Test-clean a select spot on your wall. Pick an area that is blocked from view by furniture or otherwise hidden. Wet a sponge in your mixture and squeeze it until the excess water has been wrung out. Wipe the area in a circle, using minimal pressure. Repeat with a second sponge and clean water to rinse. Then pat dry with a soft cloth or towel.
Use soft sponges (as opposed to a more abrasive kind meant for scrubbing burnt food), especially if your walls are painted. Using tougher sponges could ruin your paint’s surface. Sponges in bolder colors may leave their color on the wall.
Add more vinegar if necessary. Compare the test-spot with the rest of the wall. If your mixture did the trick, use it as is. If the test-spot still seems dirty, increase the ratio of vinegar to water and repeat. Start by adding ½ cup (118 ml) of vinegar to your gallon of water. If that still seems weak, keep adding ½ cup of vinegar at a time. Extremely dirty walls may require a ratio of 2 parts vinegar to 3 parts water.
Add baking soda if needed. If the dirt on your walls has crusted over and/or built up, you may need something a bit more abrasive than just vinegar and water. Start by adding a ¼ cup (55 g) of baking soda to your solution and test-clean again. If necessary, keep doing so up to 2 to 3 cups (442 to 662 g). However, bear in mind: If your walls are painted, abrasive agents like baking soda may damage the paint, especially if it’s latex-based. If your solution starts ruining your paint job, you may need to apply a fresh coat rather than clean.