If your software is not a work of art you have failed as a software developer.
Noob developers and people with move fast and break things mentality might tell you these are only nice-to-have or academical but do not be mistaken. These are essential for mission critical software, its supporting software and software you generally expect to work and maintain. Though your mileage may vary in details depending on language, purpose, etc.
In no particular order.
code should be more or less SOLID
illegal states must be unrepresentable
code should be DRY
code should be KISS
avoids accidental complexity
unnecessary temporary variables
less moving parts reduces failure potential
is reasonably split into multiple projects, including version control repositories
inputs are parsed, validated and normalized on system boundaries
software is fully covered by unit tests
does not depend on network (besides local interface)
uses little to no fakes
faking / test data input happens through CDI
ideally only at level of public interfaces
avoiding test invalidation by implementation detail changes
lines are no longer than 74 characters to account for
terminal text editor in 80 columns with line numbers
email based review replies
must not affect naming, clarity and greppability
in case of long argument lists / function signatures consider
writing each argument on separate line
lines starting with a comma instead of ending on it
improves readability as shapes of such code structures are more unified and eyeballing the individual arguments is easier as argument separator (newline) clearly stands out (as opposed to "," in number of other tokens on single line)
makes clearer unified diffs in future changes
uses standard tools
builds in single step
does not bundle dependencies
git or better
linear history (as much as possible)
rebase before merge
no git-pull merge commits
contains good commit messages
much information can be documented through proper (sub)typing
eg. it is better to accept Nat without further documentation instead of an Int and explaining it is >0 in plain text.
lives in the same git repository as the code it documents.
uses standard and apropriate format
reStructuredText or better
written following the same principles as code (mostly)