Sketching Car Interiors is not an easy thing to do, compared to exterior sketching interiors are more complicated. The relationship between empty and full spaces is completely different, for beginners I suggest the “BOX” method.
You sketch a box in the right proportions and later start sketching the interior of that box so it will be easier to manage all interior elements to draw (dash board, consoles, door panels at so on…).
Here a great video that shows well how to do!
Enjoy.