How do I learn AppleScript?

Probably the best approach to learning AppleScript is to buy one of the available AppleScript books or the Scripting Kit and work through the scripts in the book. Constantly fooling around with AppleScript also helps. Because Apple event and object model support in third party applications isn't always consistent, you will quickly discover that what works in one program may not work in another. Experience is the best teacher in these cases. Another avenue for learning how to script is to study the scripts that others have written. Look at the example scripts that are supplied with the Scripting Kit. You can also watch the progress of Apple events in the Log window (AppleScript 1.1) to learn more about how scripts work. If you are using one of the third party script editors (Scripter or Script Debugger), you can watch the variables as they change.