#1 – Talking too much. You should aim for the 85-15 rule: 85% listening and 15% talking.
#2 – Failing to prepare. Do not improvise reading a CV for the first time in front of the interviewee.
#3 – Asking questions off the cuff. Don’t play it lose and come up with some questions beforehand.
#4 – Not knowing your legal limits. Make sure you do not cross and legal boundaries when asking or talking with an interviewee. E.g. avoid all personal questions.
#5 – Being blinded by personal preferences. I personally think biases are one of the main problem with recruiting nowadays.