Apple has a Developer article on Bug Reporting Best Practices
which includes tips for writing meaningful descriptions, and individual tips for more detailed reporting of bugs in Xcode, Java, Safari, Mail, iChat, Audio, USB/Firewire Ports/Drives, AirPort, iPod, iDVD. The information was also presented at a WWDC session this year (I was at another session at the time).
Interesting tips include using
sample (Application Name) 15
to ‘sample’ hung applications.
There are also instructions for turning on more bug reporting in iChat and Mail.App.