Because an OPI (see: What is an Oral Proficiency Interview?) follows a conversational format and is not based on a particular textbook or syllabus, there is no way to predict exactly what questions or topics will come up:
Practice conversation and role plays in your conversation sessions. These might be simple interactions or more complicated ones, depending on your level.
When a student does an Oral Proficiency Interview, a rating is assigned based on the ACTFL Proficiency Guidelines for Speaking. You can look at ACTFL’s Can-Do Statements for Interpersonal Communication to get some ideas of topics and situations to practice at different levels.
If you have taken an OPI in the past (perhaps at the end of the previous semester):
For more information about the proficiency levels, see What are the ACTFL Guidelines?, or you can read descriptions of the proficiency levels on ACTFL’s website. ACTFL also has videos of English speakers at different levels, so you can get an idea of what a Novice, Intermediate, Advanced, or Superior speaker sounds like.
NOTE OF ENCOURAGEMENT: When you take an OPI, you should be aware that the interviewer will ask some questions you cannot answer. This is perfectly normal and does not mean that the OPI is not going well. The interviewer needs to find both the “floor” (what you can do with the language) and the “ceiling” (what you can’t do yet). So there will be some difficult questions when the interviewer is looking for the “ceiling,” but you don’t need to worry that you are doing poorly just because you can’t answer every question.
You may also want to read the articles under Strategies for Conversations.