So you have made the decision, Barcelona it will be, but you have no idea what to do to prepare yourself for the move nor your new expat life in Barcelona. When we decided we were moving to Barcelona in the year 2000, the Internet hardly existed and so we didn't have Facebook groups or blogs with experiences from thousands of people who had already gone trough the same experience. We simply had to discover our own way by trial and error. Luckily, I'm here to offer you advice for your move to Barcelona, Spain.
You will have to find a good removal company to bring your stuff over to Barcelona. Before starting to pack, you might want to take advantage of this moment and throw out things you wont be needing anymore like too many sweaters and coats and boots. Keep some because you will most probably visit the mountains nearby Barcelona, but you wont need as many as you have now.
If you don't dominate the Spanish language, I strongly recommend to start a course, as speaking Spanish is the only way to truly integrate into the country, make friends and to find work. And though not the main language, don't underestimate the importance of the Catalan official language that is spoken in Barcelona and the whole of Catalonia.
You will have to find yourself a place to live, either by buying a house or by renting one. My advice would be to start renting so you can find the ideal place for buying if that's your intention. When you want to rent, take into account that in Barcelona city this is hard and expensive because there is much more demand than there is on offer. Normally you need a contract that shows that you are working here in Spain, as a guarantee that you'll be able to pay the rent every month. Beside that, you will have to pay one month of rent as a fee to the agency that found your house and it's also normal that you will have to pay 3-6 months rent as a security for damages or not paying your rent. I hope you've been able to safe some money!
You will have to get yourself insured as soon as possible once in Barcelona. At least everyone will need a combination insurance of: private liability, travel- and content insurance. Most people will have to insure a car or a motor/scooter in Barcelona and even though you might be covered by the governments Social Security for your health, I strongly recommend you to also take out a private health insurance. Last but not least, you might want to consider a funeral insurance. Suppose something would happen to you, your family probably would like your burial to be in your country of residence but moving a body costs around 6.000 Euros and that is apart from the burial expenses. With a cheap funeral insurance for expats, this financial risk will be covered and you wont burden your family with extremely high expenses. For all expat insurances, please see www.orangeinsurances.com/en/.
If you're planning on staying her for a longer period, you'll have to become a resident in Spain, with a NIE (Número de Identidad Extranjeros). It's not that easy as it was in our time, to get one but as a European citizen, it's not impossible either. You will have to demostrate that you either have a job, or a lot of money on a Spanish banc account or you will have to show that you have a private health insurance in Spain. Most insurance companies don't accept you as a new client as long as you don't have a NIE, so that way it's hard to get a private health insurance. The company that we work with (Caser) does accept you for this insurance without a NIE.
When you want to get married in Spain, you will have to proof that you haven't been married in your country of origen. How this works depends on each country, but we had to go to the Dutch Ambassy to declare that we weren't married in the Netherlands and in no other country and that was all (though we had to go to hell and back to find this out!).
Don't forget to get unregistered in your own country, make sure you're no longer obliged to pay taxes there and they know that you're living in Spain! Do things correctly in order to prevent problems in the future.
Finally, you'll want to organize a farewell party for family and friends, since you'll miss them and they'll miss you too! Stay in touch through all social media options there are today. Though you'll make a lot of new friends in Barcelona, never forget the ones you already had before you came here.
Good luck and welcome to expat life in Barcelona!