I am writing a lot of documents mostly with mathematics in them.
I personally leave 1cm space between sections/subsections etc and the text below them and a 0.7cm space between text and math formulae. Also an 0.3cm space between paragraphs. I have adjusted these values only because I like the output.
There are a lot more customizations that I use for example I always use \displaystyle (although there are a lot of you that have warned me against it and I believe that there is a good reason for it, but I really like it), also I don't want to mix text and math so I generally place math in a new line (with a space of 0.7cm as I said).
Sometimes I make up my mind and I change the spaces I use or some of the other customizations...
So I would like to ask all of you writing documents (books included) is there any special way or special rules that someone must follow for the size of the formulae or the spaces or generally for the output? Are you following any guidelines? When someone is being given a manuscript to typeset does he do whatever he likes based on the output or is he following some rules?
For instanse when I want to write different sentences I leave a space of 0.3cm as you can see:

\displaystyle) inside paragraphs, and so on. You need to provide some information on these subjects to give anyone a chance to judge, say, whether 0.7cm vertical spacing around equations is OK. – Mico Oct 20 '14 at 05:31First your question implies a not very common orthotypographical domain in mathematics. I don't remember seeing many books about it, I know of one that can come in handy and help dispel doubts just I don't remember the title name right now. You'll have to wait until tomorrow I can go to the library and see.
Secondly, your question has to do with style conventions that may vary from country to country, or from language to language, not to mention from publisher to publisher.
– Aradnix Oct 20 '14 at 05:45TeXwas created by someone with a pretty good typographic culture, although it is not perfect, he was careful to take care of the proportions between the different elements that compose it refers to mathematics rather than precise dimensions in these items. – Aradnix Oct 20 '14 at 05:46\abovedisplayskipwhich sets this length but you never need to set it on a per-document basis, it should be set in the document class as part of the overall design) – David Carlisle Oct 21 '14 at 00:18\begin{theorem} $P=NP$\end{theorem}the spacing around theorems is an aspect of the document design and should not be anywhere near the actual document text. – David Carlisle Oct 21 '14 at 00:37\vspaceetc? the paragraph space should be set globally (or in the definition of an environment) – David Carlisle Oct 21 '14 at 01:19\vspacewhat is the right way? I mean is this even considered a paragraph? It is just a simple sentence... – Adam Oct 21 '14 at 01:19parskip. From what I understand is that this is to achieve the 0.3cm between the paragraphs that I want. When can I set that? – Adam Oct 21 '14 at 01:24\begin{document\setlength\parindent{0pt}\setlength\parskip{0.3cm plus .1cm}(best allow some stretch) but better use something likeparskippackage which lets you do this without messing up "hidden" paragraphs in section heads etc – David Carlisle Oct 21 '14 at 01:27