Migrations fail in the planning, not the copying. Here's what the plan has to include.
Moving to Microsoft 365, or restructuring within it, is one of the highest-stakes projects an organization runs. The copying is the easy part. The decisions around it are where migrations succeed or fail.
Inventory before you move anything
You cannot migrate what you have not mapped. A real inventory covers every source, file servers, old tenants, Google Workspace, Dropbox, personal drives, plus sizes, owners, permissions, and what is actually still in use. Migrating without it means discovering surprises mid-project, which is the expensive time to discover them.
Decide what not to migrate
The cheapest data to migrate is the data you leave behind. Most environments carry years of duplicates, abandoned drafts, and obsolete records. A cleanup pass before migration, not after, shrinks the project, speeds up the cutover, and means the new environment starts clean instead of inheriting the old mess.
Design the destination first
Lifting an old folder tree into SharePoint as-is just relocates the chaos. Before anything moves, design the target: which sites and libraries exist, how permissions are structured, what the naming standards are. The migration then becomes a mapping exercise from old structure to new, documented, reviewable, and testable.
Protect the things people don't think about
Files are the visible part. Version history, metadata, shared links, and permissions are the parts people notice only when they are gone. Your plan should state explicitly which of these are preserved, which are rebuilt, and which are intentionally dropped, agreed before cutover, not litigated after.
Pilot, then move in waves
Migrate one team first. Validate counts, spot-check permissions, let real users work in the new structure for a week. Every issue the pilot surfaces is an issue the remaining waves avoid. Big-bang cutovers look efficient on a timeline and rarely are in practice.
Plan the people side
A technically flawless migration still fails if nobody can find anything on Monday morning. Short, role-specific guidance, where things live now, how to share correctly, plus a visible place to ask questions during the first weeks makes the difference between adoption and quiet rebellion.