Thanks for following my works :) I've actually made some more 12x12 tiles which I haven't shared yet since I feel they are still half-baked. But for my workflow, I'd feel best to generalize it as aiming for a 3/4 top down rpg perspective (since this is what usually comes up as a common term) where you show the top and front plane, and sometimes a portion of the side (which takes space on the top/front plane) depending on the shape of the object.
I don't think I can explain the projection style technically so I'd recommend cyangmou's reference as a starting point:
https://cyangmou.itch.io/isometric-games-dont-exist
The caveat is I tend to see a lot of tilesets that mix and modify the views within the same tileset (and still look great) so it's more of a style and consistency issue. Generally I focus more on these considerations when working:
1. Full buildings don't necessarily have to scale realistically but elements such as small objects and entrances should try to be proportional to the character sprite size e.g. character width/height should fit through doors. (which is why I've been focusing on creating characters first lately). Not a hard rule, but technically you can create 12x12 tilesets that fit to different character sprite sizes depending on how you size your elements.
2. The biggest roadblock on my end would be applying standard tileset patterns to make your tileset modular and usable for auto-tiling in most cases. For expandable tiles like grounds or cliffs, I would generally slice them into 9 tiles for the top and/or front plane so you can expand them in all directions. Some references to start you off with:
https://www.boristhebrave.com/2021/11/14/classification-of-tilesets/
https://www.sandromaglione.com/articles/how-to-create-a-pixel-art-tileset-comple... (has two parts)
I haven't really focused on tilesets yet so hope this helps somehow.
