We've had posts on how to collect business cards at networking events and informational sessions. Remember to have a casual conversation and try to get to know each analyst or MD beyond work. If given the chance, talk about where you grew up, where you like going on vacations, what music you listen to, any interesting books you read lately. MDs don't forget it students that have shared interests.
To illustrate, a politics student at an East Coast university talked with an alum, an MD at a bulge bracket firm, about recent elections. The student had worked on the Obama campaign, while the alum had worked on a campaign one summer as an undergrad. The alum mentioned a fundraising event for a candidate, and invited the student to attend even before the student had followed up. The student attended, had built a strong connection with the alum, and got to learn about the alum's job and the industry as a whole. This was the student's "way into" banking.
What should you take away from this?
At informational sessions on campus or at networking sessions, there are always a huddle of students around each analyst or MD. Do have your questions prepared, and also listen in on what they are saying to other students. If the MD and analyst are alums, they are bound to talk about what it was like being an undergrad -- what clubs, teams, classes they were a part of -- and you can strike up a more personal, enjoyable conversation based on the alum's interests.
Maintain professional presence and talk as if you would to a professor you know well. By striking the right balance between professional drive and being personable, you stand a greater shot of landing your dream job.