1) Ignore the user report… even those of savvy users.
2) Read every word of the error
3) If there’s no error, find the error. (There’s always an error message, unless you’re dealing with a virus, in which case proceed to step -100, which is “Stop using Windows”)
3) Continue ignoring the user report
4) Consider the context of the error
5) Ask yourself questions that links the error to the context
6) Step away
7) Come back, and fix it
8) Consider the user error, so you know what to tell them beyond “it’s fixed”