How should a fresher prepare for his first interview?
The key is to always prepare effectively for a job interview. That way you minimise the unexpected questions and then you can take bullet point notes in with you to remind you of your best answers.
Start by studying the Job Description & Person Specification (if there is one), plus the job advert / interview invite info and the website of the organisation concerned. Logically these should give you all the "clues" you need to start guessing the kinds of skills & competencies required in the post. The interview questions should be about these.
After this start thinking more broadly about the organisation, its values, "market place" / sector(s) it operates in and what context it's working in. The more you know about them and their market circumstances the easier it will be to "pitch" yourself as a good candidate