I lived in Rome, and knowing Italian was a big plus of my daily life, being able to make informed decisions about the products I buy and chat with the butcher and the kebab guys. On top of boosting your social life, it also opens up the possibilities in terms of lodging and, I expect, work. That being said, since I had a good handle on the language by the time I moved to Rome (for a semester of university), I wished I could practice it more; however, the people I studied with were learning French (my first language) and were eager to discuss with me in this language. Other people around town were also very quick to switch to English if they saw me hesitate just a moment. For this, I would have preferred to live in a small rural town, where people I meet would not even think of talking to me in a language that is not Italian! That would be for sure the best way to make fast progress, I think.
But yeah. If you go, you should learn and practice as much as possible first. Practising becomes less efficient if you don't have a good basis already!