This answer focuses more on minimalizing the code, rather than finding the source of the problem, as the top-voted answer does. It is intended to be concise and hands-on, but digestible rather than exhaustive. Suggestions for improvement welcome!
Here are some strategies for reducing your code, which will help you get better and faster answers, since it ...
In my experience, the OP does not always choose a title relevant to the problem s/he's facing. Example:
Tex doesn't work
A poorly chosen title is, of course, forgivable in many cases; the origin of the problem may not be obvious.
However, someone posting an answer that solves the OP's problem, or any subsequent visitor to the page who is savvy enough, ...
Proposal for Acceptable:
Updating code in old answers following software updates (e.g., a new package version)
Provided that the original code is preserved, to facilitate users with older versions and to show the effort of the original answerer.
See also Updating an old answer when my knowledge improves, or a package is updated.
I think I could add prof. van Duck's tutorials.
Section 3 Asking effective questions on TeX.SE of his first article in TUGBoat 38:3, 2017 explains how to build an MWE.
Section 3 How to format a post in TeX.SE of his third article in TUGBoat 39:3, 2018 explains how to format your question.