Giovani, would you happen to have a Skype account? If so, I would really like to talk to you. You seem to know a lot about linguistics judging from another post that I read from you. Linguistics, among many other things, is one of my greatest passions. I've studied French, Japanese, Mandarin, Arabic, Hindi, Korean, Tagalog, Swahili, and a little bit of German. I grew up speaking Spanish, and find the language to be very interesting. You see, my family originally speaks what many people call Mexican Spanish. This can obviously be considered a dialect. However, I have also become very interested in the many existing variants of the language. For example, Castilian Spanish, as it is formally taught in official curriculum, has an interesting inclusion of sounds that are not present in Latin American derivitives. Similarly, Cuban and Puertorico accents tend to omit the s sound at the end of words. As for your original question, my recommendation for learning any language is to get a good grasp on some of the foundational grammar. Also, although many courses leave this out, I would strongly encourage you learn the common colloquialisms that will be encountered in a particular country. However, overall, a generic technique to improve vocabulary and to enhance the understanding of grammatical constructs is to simply listen to media and/or native speakers of the target language. A good introduction course to the Spanish language is available from Pimsleur. In my personal experience, getting a little bit of practice every day really helped me to understand many of the language that I know today. One major example is Korean. I learned a bunch of Korean grammar, vocabulary, etc just from watching some K-Dramas and listening to K-Pop.
Anyway, this message is getting a little too long. Let me know if you are interested in speaking to me about any linguistics topics. Unfortunately, I am swamped with university work and related matter. So, it will be some time before I'll get a chance to revisit this forum.