Start the interview on time: This first meeting will set the tone for your future working relationship
Make eye contact (if over video): Do not be so buried in note taking that you forget to engage with the person.
Be humble: No matter how well the candidate performs answering the questions they candidate should feel like you are working with them to assess their skill, not showing off your own.
If the candidate gives anything but an optimal answer, encourage them to improve. Ask them for an analysis of the performance of their answer. Ask what they can do to make it better.
Encourage candidates to think out loud and give them space to think. Some people need silence before answering a question. Give them that silence.
If the candidate did not pass the interview, they still might be a contributor to your Open Source Project and they may also be a source of referrals for other candidates. Be kind and considerate to EVERYONE.
10 mins: Introduction