What makes something relevant to an argument and how can people improve in determining relevance? Are there any books that examine questions about relevance in general like the following?
Relevance Theory seems something else and inapplicable.


What makes something (ir)relevant to an argument or discourse? 
How can humans improve on deciding whether something is (ir)relevant?
The Wikipedia article on relevance references a couple of books and a few journal articles.

The Wikipedia article says


  Cognitive science and pragmatics
  
  Further information: Relevance theory
  
  In 1986, Dan Sperber and Deirdre Wilson drew attention to the central importance of relevance decisions in reasoning and communication. They proposed an account of the process of inferring relevant information from any given utterance. To do this work, they used what they called the "Principle of Relevance": namely, the position that any utterance addressed to someone automatically conveys the presumption of its own optimal relevance. The central idea of Sperber and Wilson's theory is that all utterances are encountered in some context, and the correct interpretation of a particular utterance is the one that allows most new implications to be made in that context on the basis of the least amount of information necessary to convey it. For Sperber and Wilson, relevance is conceived as relative or subjective, as it depends upon the state of knowledge of a hearer when they encounter an utterance.


The books referenced are:

Sperber, D. &amp; D. Wilson (1986/1995). Relevance: Communication and Cognition 2nd edition. Oxford: Blackwell. ISBN-13: 978-0631198789Available from:
Amazon UK
Amazon US
Amazon Canada

and

Sperber, D. &amp; D. Wilson (2004). Relevance Theory, In: Horn, L.R. &amp; Ward, G. (eds.) 2004 The Handbook of Pragmatics Oxford: Blackwell: pp 607-632. ISBN-13: 978-0631225485Available from:
Amazon UK
Amazon US
Amazon Canada

There is free access to this part of the book on Dan Sperber's website

When going to the amazon pages for the relevant books, it also suggests other books other people have bought with these books along with other possible related books.