When a bug or problem arises, one must often seek out the corresponding error-messages or error-logs. Since Civi runs on a large stack, there can be several layers to check, e.g.
- The Civi application log
- The PHP error log
- The httpd log
The answers vary a bit (depending on CMS, browser, server platform, etc), but there's also a fairly limited range -- in general usage, there are only a handful of common CMSs (Drupal/Joomla/WordPress), common browsers (Firefox/Chrome/Safari/IE), and common server platforms. For web-designers and moderately-technical site builders, it would help to have a cheatsheet with common places to look.
I found a couple pages about debugging strategies in Civi. The bug-reporting page discusses the high-level business process of using forums and issue trackers. The Debugging for developers page is very developer-centric (eg adding new log statements to the source-code; installing+configuring xdebug). However, I could not find a concrete list of places or instructions for checking logs.