I used warm soap and water, Simple Green, Oil Eater Degreaser, mineral spirits, and some Macquire's Vinyl cleaner. I used several different bristle brushes, but you need to be careful as you can remove the grain if you really scrub hard.
Mostly I would spray the panel with one of the cleaners (soapy water, degreaser, simple green, Macguires), then wipe it in with a rag dipped in warm water. Let it sit for half an hour and scrub/rinse it off. I'd let it dry, then move on to the next cleaner. After 2 or 3 cleanings I'd rub the whole panel down with mineral spirits and let it set. I had the panels out of the car for 2-3 weeks cleaning them all.
This is what they looked like before and after:
Seat hinge covers:
Door panel:
For the black panels (console, kick panels, etc) I followed the same cleaning regimen and then I applied about 6 coats of Macguire's Back to Black. This is rub on, let sit, rub off. After the panel dries, repeat. This really helped to even out the color and eliminate the dulling.
This is a side by side of the treated console, and the untreated door (both had been cleaned just no b2b applied to the door)
Close up:
