Is there a best practices guideline for writing man pages?
What should be included in the layout? The standard ones are:
NAME
SYNOPSIS
DESCRIPTION
EXAMPLES
SEE ALSO
There are others like OPTIONS, AUTHOR.
As a user what would be useful to have? What isn't helpful?
If you cannot find any old bound copies of 1970s Bell Labs "troff" documentation, which had some nice sections on writing man pages, :-) then I'd suggest trying out Jens's "HOWTO" on writing man pages over at his site.
The Unix 7th Edition manuals are available online in a variety of formats.