How to construct a BNF for a language mechanically and incrementally?

[Peng Yu]

It seems to me that to use bison I have to have a BNF first. I'm
reading Programming Language Pragmatics 3rd Ed (PLP3). What is not
clear to me is that how to construct the BNF for a language? Based on
my reading of PLP3, I haven't found a formal way to construct BNF.
What I understand is that, to construct a BNF, I'll have to think
about some examples written in the language and write the BNF based on
my experience.

A language definition is usually evolving. It is not clear to me
whether it always affects the BNF incrementally if the language is
changed little by little.

Please excuse me if my questions have been answered by some books or
previous discussions. Could somebody let me know how to details the
two issues?