Think back to past situations
The best preparation for behavioral based interviewing is to brainstorm ahead of your interview specific situations you have been in, in the workplace. These situations should include a time where you were successful on a team, or a specific project, a learning experience, how you reacted to negative feedback, how you provided negative feedback, etc... You should have an idea of the type of situational questions you will be asked based on the job description of the role you are interviewing for. After you go through the brainstorming session, determine what the situation taught you, what action you took and the result that occurred from that action. You can find many examples of behavioral interview questions online, and I provided a link here to also check out.