Balboa Park is one of those places that looks like a single attraction on a map and then turns out to contain enough for several days. Museums, gardens, historic architecture and walking paths fill a huge green space close to central San Diego.
Do not try to see everything
The best strategy is to choose one or two museums that genuinely interest you and leave time to wander outside. Racing between buildings misses much of what makes the park enjoyable.
Architecture and gardens
Even without entering a museum, Balboa Park is worth visiting for its ornate buildings, courtyards and landscaped areas. Bring comfortable shoes and expect to stop frequently.
Combine it with the zoo
San Diego Zoo is located within Balboa Park, but both are substantial attractions. Trying to do the zoo plus several museums in one rushed day can become exhausting.
Plan around your interests
Exhibitions, opening arrangements and admission policies vary between institutions, so check current information for anything you specifically want to visit.
I would give Balboa Park more time than you initially think it needs. Find a bench, have a coffee and enjoy the spaces between attractions. San Diego is a city where slowing down usually improves the day.