Hi Shuttle,
There are usually 3 interviewers - two from your own fleet, one from elsewhere. Someone will ask you a lot of technical stuff - fuel policy and safety altitudes always come up, latest FCNs, plus most of the specific aircraft limitations. You may then have to prepare a briefing where one of the interviewers is 'under training' - try to speak slowly, use the white board for diagrams and make eye contact with your 'trainee'.
Try to prepare good answers to the general questions that will be asked - e.g. why haven't you applied for training before, where do you see yourself in 5 years time etc.
Good luck, and if you don't pass first time, you will be better prepared for the next try.
Y