hmm it depends, usually my process is the following:
First you start by getting to know the basic shape of it and the main structure, then add the details and decorations
Like on this example:


As for the coloring/shading process,
- Once I have the sketch finished, then I draw the flat-colored/lineless background, everything on different layers
- After that, I start detailing each area, usually I start adding the shadows and detail the textures with them, and lastly add some highlights details
- And finally when I finish detailing, I add extra lighting/shadows and a lot of overlay effects xD

here's the procces of this drawing as an example:


I hope this can be helpful to give you a basic idea!
You can also watch the speedpaint here if you're interested in seeing the full process ^_^ https://youtu.be/dqWb9FYGkGQ