Room for large work
The back takes large, symmetrical pieces: a centre design between the shoulder blades, a line down the spine, or a full back built over several sessions. The skin is firm and covered most of the time, so detail lasts well.
Because you will mostly see it in photos and mirrors, a preview matters more here than anywhere: it is hard to judge size and position on your own back.
Fitting it in the editor
Ask someone to take the photo straight on, with your arms relaxed and shoulders level. Flat is right for most of the upper back. Line long designs up with the spine, and use the Before / after divider to check the design is centred.