You’ll want to keep your Help Desk accessible by setting up multiple channels of support, including:
- Phone
- Chat/Video Chat
- VOIP
- Website
- Internal wiki, like a Google Site, to house all troubleshooting information (not just for Google Apps)
- Walk-in (clearly post your hours of operation)
Most Help Desks use Remedy or some other internal ticket system to keep track of requests. Use metrics to track support volumes, time to resolution, etc.
Another approach is to create a Google Form where users can submit their support requests. This can be posted to a Google Site or circulated via email. You can also create a Google Group for Help Desk support questions to respond to issues and share best practices.