Style guides such as those on Wikipedia, Stack Overflow, Ask Ubuntu have been greatly helpful for me (and many in those communities) in creating well-written, well-formatted, easy-to-understand, easier-on-the-eye content. So, I would like to propose a style guide for this site.
Yes, I understand that style is more of a personal preference — this is perfectly all right for well written content.
This guide is meant to avoid poorly written, badly formatted, hard-to-understand, hideous looking content; we can all spot one, can't we? And to deal with one when we spot them.
This will be a good one-stop reference for everyone who is interested.
This is a community wiki, so go ahead and edit this question and the answer(s) to best suit the purpose.