Upgrade to SQL Server 2008 - Best practice guide

Pre Upgrade Preparation

Document existing solution
Capture performance baseline data
Develop criteria and unit / verification tests
Test upgrade on pre-production/development system first
Optional: capture query plans for complex queries
Ensure Clean Environment
Backup old instance/databases and Verify
Consult and Advise your Windows Administrators, SAN Administrators and Network Operations
Optional: Access to Support

Begin by identifying your upgrade requirements
Select the appropriate upgrade strategy
Run Upgrade Advisor
Make a checklist of all issues, and then resolve all that you can before you upgrade
Develop criteria and tests that you will use to determine whether the upgrade was successful
Formulate a rollback plan
Perform the upgrade for each component you are moving to SQL 2008
Perform post-upgrade steps, including:
- Update statistics
- Reconfigure log shipping
- Rebuild full-text catalogs and indexes
- Change Compatibility Level
- Download and install updates
Prepare to implement new features