Data Migration - Do you prioritize the data that is to be imported?

Step 1 - What data?

1. Don't take all the data for the first release - Usually there are huge amounts of data in legacy systems - take only the most important firstly.
2. Using the planning spreadsheets included with the Microsoft CRM Data Migration Pack - they are excellent for specifying data migration field mappings.

Step 2 - Sync or import?

1. Syncing and keeping the old system live is the preferred option
2. Consider writing .NET callouts - or consider Scribe Insight