Golden rules of an interview:
Try to relax & enjoy it.
Listen carefully to questions - keep alert.
Have a list of questions to ask. Also ask questions/show interest in any business information they give you - for example systems you might be working on.
Don't forget to tell them about your knowledge & experience. Passing an exam already will be a big plus.
If its your first job, they will not expect you to be an expert, but they will expect you to be aware of what the job involves & what skills/knowledge you need to do it.
They will want someone keen who is willing & able to learn. In IT you need to learn a lot & keep learning (if you're going to be any good).
So its important to be: keen, alert, interested in them & the company, & able to show willingness/interest in learning.