Hey asab,
the interview process is very complicated and one of the most important that you go through.
It is your time to prove to the interviewer that what you state in your CV are true and to persuade him that you are the person for the job.
I don't want to answer your question directly and instead I will give you some tips that I've found useful.
First of all try to be relaxed and confident, if you feel very anxious (since these are your first interviews) let the interviewer(s) know it by stating it.
Always have eye contact but try not to stare, you want them to understand that you are listening and are interested.
When the interviewer(s) speaks react to what he/she is saying, let them see what you're thinking about.
Wait for your turn to speak and ask about details for the job and the company.
Be well prepared and know details about the company, how long it has been running, what is their business, etc.
And on to your question, I believe that a complete brief responce is the best.
Hope that I helped and if I think of something else I'll post
Cheers