On flat latex painted walls, if you have soot or smoke build up, the best way to clean is not to wet the wall at all, but to use what we in the business call a chemical sponge. This rubber sponge is impregnated with a chemical that removes soot and smoke from your wall like an eraser removes pencil marks from paper — only with less rubbing. This sponge can be used until almost black and will continue to remove smoke, soot and anything other than grease or oil. When soiled you throw it into the wash machine and after washing squeeze it out and let it dry — don't put it in your dryer.
Washable SurfacesFor removing other types of soil from washable walls such as enamel or finished wood paneling (not bare wood, but finished), you'll need two buckets — one with water and one with a neutral cleaning solution in it. A neutral cleaner is simply a cleaner that is neither acid nor alkaline, but pH neutral. There are many kinds of neutral cleaners. A typical neutral cleaner is dish washing liquid. A neutral cleaner won't hurt the finish on wood paneling or on your washable walls.
Turn Your Thinking Upside DownWorking from the bottom up is often a good idea — though not always necessary — it depends on how dirty your wall is and how strong your cleaner is. By working from the bottom up, you avoid the drip lines that sometimes occur working from the top down.
In cleaning, a very important principle is "Resolve to Dissolve" — rather than scrub. Following this principle, you may wish to lightly pre-spray your wall with a trigger sprayer — not enough to cause drips but enough so the sprayed-on cleaning solution has a chance to begin emulsifying and dissolving any soil and grease. By giving the solution time to work, by the time you start wiping down the wall with your sponge, most of the hard work (that is, scrubbing) has been done chemically by your solution.
In wall cleaning, to avoid using a ladder, try using a lightweight window cleaning extension wand and tools to apply solution, scrub and dry the surface.