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Prepare a little. If you can, ask for the student's resume and the kind of role they are aiming for beforehand. Skim it for projects, subjects and anything you would naturally ask about. If the programme gives you a list of sample questions or a feedback form, read it. A few minutes of preparation lets you ask relevant questions rather than generic ones.
Begin gently. Many students are nervous, and a hard opening makes them freeze. Start with an introduction and an easy question, then raise the level as they settle. The aim is to find where their understanding runs out, not to catch them out on the first question.
Ask about what they have written. A student can be expected to explain a project, a subject they list as a strength, or an internship. Avoid trick questions and rarely used trivia. You are testing how they think, not how many facts they have memorised. When they do not know something, ask how they would find out. How a student behaves when stuck tells you more than the right answer.
Give them room to answer. Silence is uncomfortable for you but useful for them, and many students need a moment to organise a thought. Resist the urge to rescue them quickly.
Give feedback that can be used. A simple shape works: one thing that was clear and worked, one thing that was not clear, and one thing to practise before the next interview. Be specific: 'Your explanation of the database design was clear. When I asked about testing, you said you tested it, but did not say how. Practise describing two test cases.' General remarks like 'be confident' are not much help.
Be honest and kind together. Students can handle truthful feedback if it is respectful and specific, and they value it. Do not flatter, and do not criticise personal characteristics such as accent or appearance.
Know your limits. Do not promise jobs, referrals or recommendations. Keep what you learn about students private, and follow the programme's guidance on contact outside the session. If a student seems very distressed, treat it gently and let the organisers know.
Afterwards, write a few notes for the programme if asked. The patterns you saw across students are valuable to the college too.