I don't know if a topic on this have been written before, but I haven't seen one. Anyways let's get to it.
INTRODUCTION Quoting a user or anyone else is a vital point in this forum, it can also be used to avoid plagiarism by quoting the original source of the information or post made as illustrated in this
thread, and
this I'll talk briefly about quoting.
When I started in this forum as a newbie, I had issues with quoting, I really didn't know how to quote properly, this is one of the mistakes I made(zoom in to see better):

The first image is the mistake I made as a newbie.
The second image is the deletion and the correction message I got from the board moderator.
The third image is a similar mistake done by another newbie.
FORUM RULES ON QUOTINGThese mistakes clearly violate rule 32 of
Unofficial list of (official) Bitcointalk.org rules, guidelines, FAQ that says;
32. Posting multiple posts in a row (excluding bumps and reserved posts by the thread starter) is not allowed.
This mistake leads to either immediate merging or deletion of the follow up posts, so when quoting multiple users, put all your quotes in a single reply in as much as the posts you are quoting are before your reply, if it is after your reply, you can quote them separately so as to avoid posting multiple posts in a row.
but there is also a good advice on this forum, like the one from
Fillipone where he said
Corollary: Quote politely: bad quoting can worsen the reading experience of other users. Quoting the whole message to answer only a specific part below, or answer a few question all below the quoted text are bad practices. This is something not related to this forum specifically, so you might already know about what I am saying here. If you don't please get used to best quoting practice reading one of the many good guides out there, like this one.
QUOTING EXAMPLESYou can edit your quotes as much as you like, highlighting and or keeping only what you want to specifically talk about, it is really flexible, here is another thread that talks about proper quoting,
[TIPS] to avoid pyramid quotes (for Newbies).
There are 2 required things that makes up a BBCode quote, and 3 optional parts, they are;
1) Opening quote tag
2) Closing quote tag
Optional features:
3) author: Owner of the quote you are quoting
4) link: direct link to the quote you are quoting
5) date: date when the quote you are quoting was made in unix timestamp.
E.g
Without link and date:
[quote author=quote owner] ===> opening tag
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
[/quote] ===> closing tag
Your reply
With link and date, you can click the quote button on any post and you will have the full feature.
This will look like
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Your reply
E.g for multiple quoting
[quote author=quote owner1]
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
[/quote]
Your reply
[quote author=quote owner2]
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
[/quote]
Your reply
How it will look like:
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Your reply
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Your reply
TL;DR:
1) Avoid posting multiple replies in a row just to quote different users.
2) Edit quotes to keep only the relevant parts you are talking about.
3) Avoid long pyramid quotes as much as possible (i.e. multiple nested quotes).
4) Always reply under the quote for clarity.
Note: the same topic might have been out there, but I searched and didn't see, my main purpose of doing this is to educate newbies on how to quote because this is like one of the newbie's mistakes I've seen, if this constitute a spam in any way, mod please go ahead and delete, thanks.