Overview

Based on "The Pragmatic Programmer" by Andrew Hunt & David Thomas. Hunt & Thomas's debugging philosophy: debugging is a puzzle to be solved with evidence, not a crisis to be panicked through. The key discipline is don't guess. Form a hypothesis, predict what you'll see if the hypothesis is correct, test it, and observe. Repeat.

Their rubber duck principle: before asking for help, explain the problem out loud (to a rubber duck or anyone). The act of articulating often reveals the answer.

Workflow

Step 1: Reproduce the bug reliably

You cannot debug what you cannot reproduce.

What exact steps produce the bug? Document them.
Is it 100% reproducible or intermittent?
On which environments? (dev only, staging, prod?)
Since when? (what changed recently?)

If you can't reproduce it reliably, make that the first problem to solve.