Is there anything I need to do to prepare for the migration?
Yes, is it recommended that any files stored locally on your computer, outside of the OneDrive folders, be moved/copied into the OneDrive folders. Moving the files will ensure inclusion in the migration. The reason to include them in the migration is to ensure that these files get backed up daily. The backup is helpful in cases when you might have a system failure.
Also, keeping items in OneDrive allows you to have access to these files when you are away from your computer.
Outside of managing your files, there is nothing else to do to prepare.