List your deployment goals and bear in mind the following factors:

• Who are your internal and external teams?
• What is the scope of the project?
• What will be the tracking mechanism of the project?
• What are the milestone dates?

Then start making decisions about the deployment:

• Make an inventory of what will be migrated from each workload to Office 365:
  • Users
  • Groups
  • Mailboxes (if it is a mailbox migration)
  • Computers (operating system, Office client version, and patches)
  • File shares (if it is a SharePoint or OneDrive migration)
  • Intranet sites
  • Instant messaging
  • Web conferencing
  • Audio conferencing
  • Voice
  • Third-party applications that are integrated with the current systems

After you have all the data about what type of migration you will perform and the workloads that are to be migrated, you can make decisions that are relevant to the project.