How to Answer Investment Banking Behaviorals
You should use some version of the STAR framework: Situation, Task, Action, and Results.
Use the STAR Framework
The STAR framework is not rocket science. Just walk the interviewer through the situation, task, action, and result with a sentence or two dedicated to each letter. Some people like to include another sentence after the result where they explain why the story is relevant or important for the role. For example, one story may display your independent thinking, which is important because analysts are expected to solve problems without constant hand-holding.
The framework is useful because it keeps your answer from rambling. Briefly explain the situation, describe your responsibility, walk through the action you took, and end with the result.
Add Personality
Lastly, try not to be boring. Interviewers hear the same stories about the group project with the bad teammate, or that one particularly hard class, over and over again. Try to add some personality into your answers and, importantly, smile during the interview.
Practice Out Loud
Just like technicals, practice goes a long way when answering behaviorals. It is very easy to start rambling, stuttering, or making up parts of your answers when pressured on the spot. I would recommend either recording yourself or doing mock interviews to practice these aspects.
This will also help you prepare for HireVues because you get used to answering clearly without immediate feedback from another person.