Spain's major cities will undoubtedly offer the most opportunities for any foreigner looking to work in the country. You should bear in mind that finding employment in Spain is often down to who you know and not how qualified you may be. Nevertheless be sure to find out if the qualifications from your home country will be recognised.
Being a foreigner can be a disadvantage in some industries and with some employers; there are also restrictions regarding employing foreigners in Spanish business.
If you do not have a working knowledge of Spanish, your employment possibilities are going to be especially limited. Learning Spanish will be invaluable to your job hunt and would definitely increase the number of opportunities available to you; it is also an excellent way to ingratiate yourself with any potential employers. Furthermore, if you are looking to work in Cataluña then at least a basic understanding of Catalan is a must.
There are some industries, however, that continue to look for skilled foreign employees. Skilled trade workers, engineers and those experienced in the finance sector are currently in demand. There are also plenty of opportunities if you want to be a teacher of foreign languages, especially English.
Due to the current economic climate and high unemployment in Spain it is strongly advisable that you have a job in place before you move.