I think it really depends on whether you’re just trying to show off your character or if you’re trying to tell a story. If the character design is the main focus, it’s often better to use a plain background such as a color gradient and some vignette, and perhaps some smoke or particle overlay behind the character. This keeps the background from distracting from the character. If you’re really trying to tell a story, I find it useful to brainstorm this when you first start designing the character. Think about what pose and setting you’d like to see them in, and use that to your advantage when modeling/texturing/lighting. Personally, I think that if you want to see your character in a scene in order to give them some story and life, it is worth your time to design and model your own background/scene so that it conveys exactly what you want it to. But generally, you don’t want the surroundings to distract from the character, so keep it subtle and make sure your character is separated from the background by using color, depth of field, etc. A great source of reference for these two approaches for backgrounds is on ArtStation. Sort by Picks and Digital 3D, then sort either by ‘Characters’ or ‘Story Telling’ and note the differences. Good luck!
