It depends on what kind of approach you want to go with. There are actually a few ways to go about cleaning the interior but here are the two most common:
1. Pre-spot tough stains, then mist entire area with
APC or carpet cleaner. Agitate. Rinse. Extract.
2. Pre-spot tought stains, mist entire area with
APC or carpet cleaner. Steam and agitate with microfiber.
These are pretty rough guidelines to cleaning an interior and everyone has a slightly different way of doing it. Good luck!