There are always events being planned in and around the area of the University. Many of these events are culturally based, while others lean more towards specific interests, such as a type of music through history or a session all about French wine or cheese. Magazines usually advertise events like these and sometimes a small commission is charged for entrance (which can be discounted if a student card is shown). The Champ de Mars becomes an amazing hangout when the weather is nice. Some of the Parisians don't mind when students practice their French on them and probably more than one student has been astonished when a waiter on break urges them to keep up a conversation in broken French.
Try to keep away from people who walk around selling souvenirs, as you will probably feel cornered into buying something and most of them will push their luck in trying to get you to pay more than what it's worth. Keep away from groups of people from outside of Paris who look like they are looking for trouble. If they are, then you'll most likely figure that out within a few minutes of seeing them. Also, be careful about where you open your wallet, as you will probably attract some people begging for money who are sometimes difficult to get rid of if you don't speak French.