If you want a gentle wall cleaner, warm water and washing up liquid will do the trick. This concoction will remove general scuffs and marks without damaging the paint in the process, leaving you with clean walls that are still in pristine condition.
But if you have tougher stains that you want to tackle, you’ll need to incorporate even more products. What you use is down to you, though. You could opt to use vinegar, baking soda, sugar soap, or products designed specifically for such tasks, including Magic Erasers and specific wall cleaners.