An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons)

What is the best way to setup an error page so I can view what the actual error is instead of the following error?
Runtime Error Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons). It could, however, be viewed by browsers running on the local server machine.  Details: To enable the details of this specific error message to be viewable on remote machines, please create a <customErrors> tag within a "web.config" configuration file located in the root directory o ...