Begin with Sagrada Família.
Give the basilica your freshest attention and avoid stacking another timed visit immediately afterwards.
One-day itinerary
A realistic route through the essential works, with breathing room built in.

Visit with intention
Give the basilica your freshest attention and avoid stacking another timed visit immediately afterwards.
Allow time for the journey, the monumental area and a pause rather than treating the park as a quick photo stop.
Choose Casa Batlló or La Pedrera. Seeing both in one day usually adds repetition and removes the pleasure from the route.