Ok,
It is pretty simple. Firstly, I decided that I would use a sand color because TD 6926 is a Sandtrooper.
Then I decided that proper dirt does not cover an item the same from top to bottom. A person walking in the desert has dirtier feet and legs, their chest and head are relatively clean.
Dirt accumulates in recesses and crevases, I gave these areas a bit more paint. Edges and exposed areas are relatively clean, so I rub the paint almost completely off these areas.
I picked an acrylic sand colored paint because acrylic is water soluble and I can erase mistakes and "edit" the shades in various areas. I diluted the paint in a mixture of 4/5 water and 1/5 paint.
Then I painted it on a smallish section of the item I'm painting. You don't want to paint an area that is too large because it will dry before you can "smudge" the color.
Then I "smudge" the color by patting it with a dry rag. You can also "smear" the color by rubbing it over the armor.
This is a pretty good YouTube video that shows the basic technique:
I'll work on the rest of the stuff.
Hairball