There are a few different factors regarding aging methods; the surface being aged, the location of the set and the virtual age of the set.
Generally, interior walls of a set are aged with both a hand aging, like hand cleaner mixed with raw umber, and a dust age, which is a fine wash or dust age apllied with a paint sprayer. When the walls call for water aging, the aging is usually applied through a spritzer or hudson. If the aging is dimensional, products are added to create chemical reactions, which is how the bizarre and amazing aging examples are created. On a location, the surfaces are often sensitive, and dust aging cannot be used.
Some surfaces just won't accept water based aging, like metals, and plastics. Beeswax mixed with umber is a common fix for metals, and plastic is often successfully aged with a combination of spritz and umber spray can, streaming together onto the surface. Careful, that one's tricky, and you only get one shot.
Whether or not the set is outside makes a difference. Often the location prohibits standard aging products. Tempera paints are used commonly in environmentally sensitive areas. Wallpaper glue or hand cleaner mixed with umber will wash off in the rain. Beeswax aging is great, but you won't get it off a location wall very easily once you've applied it. If a location really needs aging, and the walls are too sensitive, the tuffback becomes a lifesaver. I'd look for a better location if it was that sensitive and needed that much aging...
How old is the set supposed to be? Are the inhabitants slobs? If you look around you in your every day life, you start to notice that actually, we are fairly clean creatures. We don't usually have blackened door jambs and crud along our wainscott. I see blackened jambs at the mechanic's shop or in the SPFX shop; even old abandoned bulding photos show minimal wainscot crud. But I see alot of that on screen.
Its really difficult to undo an overly aged set without repainting. And it's a difficult process to monitor, because nine times out of ten, the aging is happening while the set is being dressed and lit.