Quoting Steve Litt (slitt@???):

> To take it a step further, for gosh sakes, write for clarity. Quote
> what's relevant to your reply, including what person said it, and
> delete all quoted material not relevant to your reply. If you're
> interleave posting, please please PLEASE delete all quoted text below
> your final response so readers don't waste time looking for yet another
> of your responses.
[...]

Sally Hambridge's (then a network engineer for Intel Online Services)
RFC 1855 is 22 years old, but is still timely!
https://www.ietf.org/rfc/rfc1855.txt

One (IMO) respect-worthy modern attempt to reassess and update it:
http://www.whoishostingthis.com/resources/netiquette/#rfc1855

There have been numerous attempts at helping people interact fruitfully
with online communities, but Ms. Hambridge's is difficult to top.