Don't wing it. Sharp candidates will be put off by a shoddy interview. Proper preparation also means less chance of a slip-up, saving you that slow countdown to the end of the new recruit's probation period.
Get the room ready. Book the meeting room and make sure water, hot drinks and enough chairs are available.
Don't discriminate. Avoid questions about race, religion, disability, children and - especially with this month's change in law - age. Any bias on these grounds and you may be letting the best candidate go. And it's illegal.