This excellent article from eWeek offers best practices to consider before an enterprise begins a cloud migration project.  Key topics discussed include the following 6 areas:

1: Evaluate the Skills and Experience of Your Internal Team
2: Conduct an Assessment of Your Current Environment
3: Build a Strong Proof-of-Concept
4: Determine the Right Tools for the Job
5: Test, Test and Test Again
6: Develop a Well-Defined Cutover Plan