What if something goes wrong?

Write down the error message. Exact text is *very* helpful.
Make a quick note of where you were and what you were doing.
Look for anything that's changed.
Look for patterns. Does it only happen if you start something else first?
Be as specific as you can be -- The person you ask for help knows only what you tell them.
Try to reproduce the problem. If it isn't easily repeatable, it may be hard to find and fix. Ideally, provide a "minimum case" description.