Apply the drywall compound to the wall in clumps, wearing protective glasses and gloves. Irregular patterns are best to create an authentic look, so this means you don't have to worry about any mistakes. Sweep the trowel in different directions so you get a variety of heights and texture to your design. Let dry thoroughly, at least overnight, or longer if it is very rainy or humid, or if your home doesn't have good ventilation.
Apply the paint with a paint roller. Don't press too hard with the roller. You want the higher surfaces to be covered with paint, and the crevices to be uncovered. Choose a color that is light so you can accent the wall later with the darker stain. Light tones of yellow, orange, terra cotta or brown will all create an authentic look. Let the paint dry thoroughly.
Apply the stain to the wall with a rag, working on one small area at a time, then wipe off with another rag. The idea is for the stain to be uneven and create different tones all over the wall. Choose a stain that complements the paint color you've chosen. Wearing the glasses and gloves is especially important for this step because the stain is oil-based and has a strong smell. Work with the windows open and a fan operating, if possible, to reduce the fumes. Let dry completely.