When reporting a bug, the first aim of a report is to let us see the failure with our own eyes. Please give us detailed instructions so that we can make it fail for ourselves.
Please include screenshots whenever possible and relevant.
In case the first aim doesn't succeed, and we can't see it failing, the second aim of a bug report is to describe what went wrong. Describe everything in detail. State what you saw, and also state what you expected to see. Write down the error messages.
When your computer does something unexpected, freeze. Do nothing until you're calm, and don't do anything that you think might be dangerous.
By all means try to diagnose the fault yourself if you think you can, but if you do, you should still report the symptoms as well.
Be ready to provide extra information if we need it. We aren't being deliberately awkward.
Write clearly. Say what you mean, and make sure it can't be misinterpreted.
Above all, be precise. Programmers like precision.