Complex sentence: He has been serving Bhartiya Janta Party (BJP) since 1989 when joined party as a devoted worker and fulfilled various major responsibilities in Kanpur BJP with best of his potential and devotion towards party.
Split into simpler sentences: He has been regularly serving Bhartiya Janta Party (BJP) since 1989 when joined party as a devoted worker. Thereafter, availed and fulfilled various major responsibilities in Kanpur BJP with best of his potential and devotion towards party.