As you can imagine, the architecture of Barcelona, the Holy Monstreat, and the Toledo cathedral make this a popular coordinate. And because this is such a hot travel spot, you're advised to make your airline reservations, hotel reservations, and car rental preparations early - three to four months in advance as a matter of fact - especially when tourism is likely to be high (summer months, holidays, etc.). If you prefer to travel "off-season," - that is, during a time when tourism is low, you may not need to make such early reservations. In the latter case, one month-advanced preparation may suffice.
After you've made your reservations, you can fulfill the rest of your time preparing for everything that Spain has to offer. One of the ways that you can do that is by taking a local trip to your favorite library and perusing the immense number of books about Spain. By doing this, you can prepare yourself with the language - perhaps even check out a few books or audio tapes of the language (if available) and additionally learn about Spain's monetary system.
You should always learn about entry requirements, inoculations and other safety information you might need before you go not only to Spain - but also just about anywhere out of the country. But you can also familiarize yourself with the dress of the land and maybe try a few local restaurants that serve Spanish cuisine and play a little of its native music. Of course you can always visit your museum and inquire about the art of the land so that you'll know what to look for once you get there - in particular, the works of El Greco. The idea here is to educate yourself amid all the excitement of visiting a place so rich in culture!
Now some people like spontaneity - a little adventure - the unknown - whatever you want to call it, but some of us like to create an itinerary of things to do and places to go. If you're the "planning type," then you might appreciate taking the time to map out your excursion. And there's certainly nothing wrong with that - seeing that you're visiting a new area, your chances of being bored or going against spontaneity are very slim because Spain has so much to offer to each one of your physical senses!