Depends on type of job but I was recently advised to go through the job/person specification and based on that to come up with my own questions and prepare answers to them.
Also - don't forget the common question "tell me about yourself and why you're right for this job".
I was also told to ensure that when using examples about experience etc to ensure that I mentioned the part I played and not to just talk about the scenario.
I was also advised that companies aren't looking for you to always know the answer but to see your thought process.
If you're asked a question you don't know - don't rush in cos the silence is making you nervous but think about the question and take your time.
If it's a problem based question a company will want to know that you're thinking about who'll you need to speak to, who will be best placed to have the info, what extra info will you need, meetings and action plans and instructing consultants etc. So even if you don't know the answer you're collating the info so you have full picture before taking action.
Good luck and don't stress you don't have to be perfect!