Update: Here’s a flowchart.

Scenario: You’re having trouble with a plugin of mine and you would like me to fix it. Here’s the definitive guide for providing a useful bug report:

Versions

Make sure you’re using the latest stable version of the plugin, installed on the latest stable version of WordPress. If you’re using older versions, you’re on your own.

If you’re using a development version of either of these, please mention which.

JavaScript

If any sort of JavaScript is involved, mention in which browsers you’re seeing the problem.

Also, mention any JavaScript errors that you encountered. If you’re using Firefox or Chrome, just press Ctrl + Shift + J to open the error console. If you’re using Internet Explorer, see this tutorial.

Conflicts with other plugins and themes

To make sure it’s a problem with the plugin itself, deactivate all other plugins and see if the problem persists.

Furthermore, try switching to the bundled theme, currently Twenty Ten.