"Without wanting to pile on the pressure, we make a note of the good candidates at our events but we also remember those who've made a poor impression. The key is to make sure you're prepared; don't just rock up thinking you can have 'a bit of a chat' with representatives from a firm.
Do your research, think about some intelligent and thoughtful questions and make sure that you tailor them to the person you're speaking to. For instance, asking me about the nitty gritty of a deal might make me doubt your common sense and how well you've thought your question through.
Firms are looking for likeable and confident trainees but don't be that person who takes this too far and gets overfamiliar (particularly after a few drinks!). I've had candidates squeezing my arm and even winking at me. You need to get the balance right; get involved in conversations without dominating them, ask insightful questions, talk to a variety of people, enjoy the free food and drink within reason and finally avoid overstaying your welcome at the end. Nobody likes a lingerer!"