Conceptual integrity defines the consistency and coherence of the overall design. In simple English, define design standards, coding convention, and have the consistency while designing all components.
To understand why conceptual integrity is important just think of few components which are using their own naming and other coding convention and not using any standard.
Common causes:
Lack of awareness that design standards or coding convention are important.
Points to be considered:
Define coding convention
Define design standards for all components
Define design principles which have to be followed