High level (assuming local storage and an allotted outage window):
1. Determine what applications (or other dependencies) connect to the server
2. Determine if the server is used for anything other than hosting databases
3. Plan an outage window with adequate time to do the following...
4. Stop any applications making connections to the databases
5. Take full (and trans log backups if in full recovery) backups of all databases including master, model, and msdb to reliable remote storage
6. Backup any other important files on the server (don't forget SSRS files, SSIS packages, etc)
7. Stop database (and any other necessary) services
8. Power down server
9. Move and re-rack/cable server at new data center
10. Power on server
11. Start database services
12. Start applications and ensure they can connect to the databases
13. Verify all jobs/scheduled backups are working correctly