Normalisation is the way to eliminate redundant data.

1st Normal Form

Remove repeated groups of fields. For Example, remove Name, Address, TelephoneNumber from a Quote entity. The groups are placed in a separate entity such as a User and replaced with a foreign Id field. For example, UserId.

2nd Normal Form

Remove any fields that depend on Id fields that are not keyed fields. For example, ProductId and ProductDescription could appear in an QuoteDetail entity. ProductDescription renamed to Description and placed in a Product entity as ProductId can be used to look this up.

3rd Normal Form

Ensure that every record, in an entity, can be uniquely identified by a key field or fields.