That's a tough question to answer... Spain is a big country. If this is your first time, why not do the tourist-thing like I did last summer? I arrived in Madrid, saw the important sites, took a premium bus to Granada, enjoyed the tapas and marveled at the Alhambra then an overnight to the Sierra Nevada for a hike and an Airbnb stay in small town. Then to Sevilla, the Pueblos Blancos and back to Madrid. If it's your first trip, see all the touristy sites. On the next trip, explore some different areas as I am this summer: Galicia, País Vasco, Navarra, Asturias and Cataluña. These regions are very different from each other and will give me a more complete image of Spain.