Below is the primary steps that you can follow when migrating data into your Salesforce instance:
Step 1. Identify each data source
Step 2. Extract data into a staging area
Step 3. Define specific rules and criteria for:
a) Cleaning the data
b) Resolving duplicate data or any other errors
c) Assigning ownership of the data
Step 4. Execute data cleansing efforts as discussed above
Step 5. Create templates for loading the clean data
Step 6. Populate your templates with clean data
Step 7. Prior to loading your data, validate:
a) Data is clean
b) Record data are accurate
c) Turn off workflow and validation rules
Step 8. After each load, validate the data is correct. Load in the following order:
a) Load users
b) Add User IDs to Account file and load Accounts
c) Add User IDs and Account IDs to Contact file and load Contacts
d) Add User IDs and Account IDs to Opportunity field and load Opportunity
e) Add User IDs and Account IDs and Contact IDs to Case file and load Cases