There's stacks of info available about interview techniques and questions to be prepared for. Things like:
- what is your greatest weakness
- describe a situation in which you had to work with somebody you didn't like, to achieve a common goal
- where do you see yourself in five years' time
Ask around your peers about what tricky questions they've been asked in interviews, and try to prepare for them and others you can think of.
But don't worry about it. Although it's not uncommon for interviewers to ask 'out of the box' questions to try to test out the candidate's ability to think on their feet, they're not out to make you fail. It's as important for them to find someone to fill their position as it is to you to find a job. When done properly, interviews are a cooperative endeavour between interviewer and interviewee to explore mutual compatibility.
One very useful prep is to research the company you're going to - what they do and a few things about their industry and environment, so you can show interest and knowledge about that, rather than just 'I've got an actuarial degree and heard you employ actuaries'. It's good to have a few questions to ask them that demonstrate that interest, as often people ask 'do you have any questions for us' at the end and, while it's good to ask about crucial things like pay, working conds and benefits, it helps to also show curiosity about how the company sets about achieving its goals and what obstacles it faces. Things like 'does such and such a market trend or new regulation have an impact on your company's operations' are good.