Here is some advice:
1) for classes try UBA and / or private teacher if you can afford it (private teacher you will lean fastest, especially if they are good). Careful with the tourist schools, most of them are pretty average quality. There are a few good ones as you will see people recommend here (just be careful of post counts, plenty of people from schools come here to provide "first hand" recommendations as well)
2) try and find an apartment with locals or spanish speakers. Even if you cant speak much at first you will pick it up as you go.
3) better than that 2, find a guy(s) / girl(s) to go out with. Español en la cama is not only probs the best way to learn, but much more interesting than learning in a class room
4) spanish music, TV etc
5) pick up a book called Che Boludo (James Brackens). Its basically a dictionary of Argentina lunfardo (slang). You mightnt know whats going on at first, but its really quite helpful.
6) importantly, dont put too much pressure on yourself, especially early. Try and enjoy it and just let it come. Its a good idea to have goals, but thoughts such as I have to be fluent in 6 months may be detrimental
Anyhoo, good luck!