Hi Nupur, March to May and September to October is best time to go to Spain. You can explore Spain itinerary here: https://goo.gl/4pyZth Keep travelling!
Hello Nupur, Precise time would be July and August, climate is awesome and you would be able to witness la tomatina and Pamplona bull run. Depending on above priority you can then visit Seville, Barca and Catalonia.