Interior Methods?

Hi,
Interiors are a poorly covered topic in most of the tutorials around and I feel that I struggle very often to bring them to the level of character or outdoor pieces I do. I have tried several different methods like:
- painting on top of a simple 3D geometry
- making a tight drawing, putting colors underneath, then painting over
- making b&w thumbnails, enlarging them, tightening them, colouring
- going straight in with colours a la prima and having spent ages tightening and fixing perspective and proportions

So, what are your thoughts on this guys, what do you find works the best?

Thanks

Practising Sci-Fi shapes

Just trying to get a few more shapes and forms into my brain.