MSPA Wiki:Manual of Style/Discussion

Signature
All messages on talk pages, and for that matter on the fora, must be signed. Place your signature at the end of the post with ~ or your custom signature template, if you have one. See the signature policy page for more details.

New topic
When starting a new discussion, distinct from whatever the one currently at the bottom of the page is about, always create a new section. If you're using the Monobook skin, this can be done on any page in a talk namespace by clicking the "Leave message" link next to the main page edit link. Otherwise, you can simply click the edit link as normal and create a new section by going to the bottom of the page and starting with a second level heading, which is created by placing the heading name between two sets of = signs. As demonstration, this very section's heading is produced using the wikimarkup,  ==New topic==

Indentation
When replying directly to someone, you should indent your reply by one step compared to their message so that it becomes visually distinct. Do this using one colon at the start of your message for every step of indentation. Posts should always be in chronological order down the page, even if that results in a post being indented less than the one above it, due to being a reply to a less-indented post further up. However, if you are replying to a post that is more than a couple of posts above yours, it may be more prudent to reset the indentation and simply refer to the post you are replying to. For example: I think that blah blah blah -- SomePerson (talk)
 * Well, the alternative is blah blah -- SomeoneElse (talk)
 * Or we could blah blah blah blah -- AnotherGuy (talk)
 * I doubt that's a good idea, but blah -- SomeDude (talk)

Actually, to expand on what SomePerson said, blah blah blah -- AnEditor (talk) results in Generally, it comes down to applying common sense to make the conversation as readable as possible while generally maintaining the indentation convention. Bear in mind also that tables can be indented, as can bullet points and numbered lists. Finally, if your message is split into separate paragraphs (either due to length or because a table/list/etc. is in the middle of it), please please make sure all the parts of the message have the same level of indentation as one another.

Conversations on user talk pages
Different users will have different preferences on this matter, but a reasonably sensible default procedure if the user doesn't instruct otherwise is to keep the entire conversation on one of the participants' talk pages (typically the recipient of the initial message), simply because many people don't like going back and forth between two pages to read one conversation. Furthermore, if more people join in on the conversation, it would quickly become impossible to track if it were spread out among the talk pages of additional participants.

That said, if a conversation on a user talk page concerns an issue that affects the wiki beyond just the owner of that user talk page, they have the right to request that the discussion be moved to a more appropriate talk page if it gets overly lengthy. A message to that effect should be given, ideally including a link to the new location of the discussion.