You have many different ways to improve your language skills and to make new friends.
First of all, about the language make an effort to speak Italian instead of English and hang out as much as you can with Italian people. Moreover, watch movies with Italian subtitles and read whatever you can in Italian (books, newspapers, essays and so on).
Secondly, there are several university associations that enable international students meeting Italian (and other international) students, such as AEGEE (https://www.aegeepisa.it/), ESN (http://www.esnpisa.it/) and, for those of you who like sports, the group Meet up, Keep fit and Make friends (https://www.facebook.com/meetupkeepfitmakefriends/). Contact them and enjoy your experience in Pisa!