Rules which help good writing style:
1) Make your new contribution longer than what you are quoting, if at all possible - conversely, quote less than what you are adding. When you respond to something, clip only the part which you are responding to. Yes, you do want enough so people will understand the context, but you can assume most people have been following the list and have seen the original post so we don't need the whole original over again. Some folks still have limited download capacity and can have their modem just crap out if the data gets too much. But also, if you're on 10 lists and need to get through them all quickly so you don't spend your whole day reading, it's nice to not have to scan through seven page-downs in order to make sure you're not missing an important point.
2) Attribute quotes correctly, by prefacing it with "so and so wrote:" or some such thing. I can't stress this too much, as I've seen many people get falsely accused of saying things which other people said, only because someone got sloppy and didn't attribute correctly.
4)Brevity is the soul of wit in sig lines. Try to get the sig line down to 4 lines, or shorter than your post, whichever comes first. If you're only adding one line of new text, get rid of it entirely, unless the point of the post is to show off your sig line to some purpose.
One-line responses are known as "metoos". They are acceptable, but should be used sparingly. When people are polling about something, or when you're someone who's agreement is important to the conversation.