One foolproof method is to maintain a field called 'Last Extraction Date' and then impose a condition in the code saying 'current_extraction_date > last_extraction_date'.

First Method: If there is a column in the source which identifies the record inserted date. Then it will be easy to put a filter condition in the source qualifier.

Second Method: If there is no record in the source to identify the record inserted date. Then we need to do a target lookup based on the primary key and determine the new record and then insert.