Collect the Raw Material
This means having a list of 1 to 10 stories or events from your life that taught you valuable lessons or showed leadership, courage, teamwork, resilience, attention to detail, or ownership.
The goal is not to memorize 20 separate answers. The goal is to have a small set of stories you can adapt to answer almost any kind of behavioral question.
Structure Them With STAR
Use some version of the STAR framework: Situation, Task, Action, and Results. It is not rocket science. Walk the interviewer through the situation, task, action, and result with a sentence or two on each letter.
Some people like to add one more sentence after the result explaining why the story matters for the role. For example, one story might display your independent thinking, which is important because analysts are expected to solve problems without constant hand-holding.
The framework earns its keep by keeping you from rambling. Briefly explain the situation, describe your responsibility, walk through the action you took, and end with the result.