Here are some studies I did for a client illustration with a goblin tribe - I wanted to work on specific things such as that monkey's skin texture and the black steel material I would use for most of the goblins' armor.
Specificity in studies, in this context (meaning outside of learning fundamentals), is what's really going to get you better at painting from invention, because it's the practical application of the theory of fundamentals in a controlled and safe environment
I also experimented with some different processes, which is always fun