Hopefully the following information will help those of you who are first-time travelers to Spain.
1.) Dress code: First of all, if you are wearing white tennis shoes, you might as well carry a sign that says, "I'm a tourist." We went during the springtime, and although the temperature was in the mid 70s to low 80s, we found that most of the people in Barcelona were still wearing coats or leather jackets, boots, and suits for men going to work. Only students were wearing jeans, and they still looked more fashionable than we did. While visiting Barcelona, we noticed how we kept getting looks because of our white tennis shoes. Now, I didn't have any intentions of impressing anyone with my sense of fashion. However, when walking through the touristy parts of town, your appearance is a red flag to pickpocketers, who hang around trying to find a bag to snatch. I personally prefer comfort over looks, but you will see what I mean. Spaniards often dress very well, so expect to stand out from the crowd when visiting this city. And if you are trying to figure out what to visit next while in La Rambla, keep your Fodor’s guide low-key. Opening up one of those is a red flag for pickpocketers as well.
2.) Dining: While in Spain, I often found myself drinking a cup of coffee after dinner, looking at my watch, and saying, "Oh my god, it's already 12am!" In Spain, people eat late. Restaurants often don't open until 9pm, with peak time being around 11pm. And forget about asking for a booth in the non-smoking section. You will inhale more secondhand smoke here than anywhere else in the world! Lunch is also late, usually served between the hours of 2pm and 5pm, with peak time being at 2pm--the beginning of siesta.
3.) Siestas: This brings me to my next topic--siesta, that time of the day when the cities become ghost towns. You will not experience as much of the "siesta time" in Barcelona as you will in other small towns, primarily because most tourist attractions remain open during this time. If you need to buy something or get somewhere, do it before or after siesta. At 2pm, businesses will not hesitate to ask you to leave so they can close down. Fortunately, most places reopen by 4:30pm or 5pm and remain open until 8 or 8:30pm.
4.) "I'm sorry for the mix-up, but I gave you a 20, and you only gave me change for a 10. . . ": More than once, especially in busy shops and restaurants, I found myself saying this. I'm not sure if they were so busy that they forgot I gave them a 20-euro bill and gave me back the change for a 10, or if they just happened to get a glimpse of my white tennis shoes and figured I still haven't gotten used to the local currency. Either way, make sure you count your change before leaving the establishment.
5.) Returning your car: We rented the car in Barcelona and returned it in Madrid. We arrived at the rental lot before the office opened. No one was there. Our puzzled looks were exactly the same as those from two other couples standing in front of their rentals. Please be aware that during after-hours, you have to walk inside the airport terminal and drop off the key, along with a copy of the condition report, in a drop box located outside the booth. Don't hand over the keys to anyone standing there if the office looks closed. Chances are they don't work there . . .
6.) Spend 90 euros or more and get a tax refund: When you spend 90 euros or more at any given establishment or restaurant, you are eligible for a tax refund. Simply get a tax form and keep the receipt. Many stores offer the convenience of giving you an instant refund. In the other case, you bring the form to the airport, have it stamped by customs, and turn it in to the IVA office (TVA) next door. Sounds like a lot of steps, but it was fairly easy.
7.) Last but not last, Spain is a beautiful country. Enjoy it while you are there. It took me a lot of research and reading from other people's experiences to learn the dos and don'ts. But you will always have a few experiences of your own. In any case, be well informed so you can enjoy your time there with no unfortunate incidents.