Ned Potter, on his wikiman blog, offers advice to the young librarian on interviews. His tie advice, though gender-specific, is sound, but does not go far enough.
This area is not as straightforward as it may seem. Give careful thought to which tie. Male junior doctors, for example, are advised to wear their medical school tie to interviews. We librarians are at a disadvantage here. Sadly the Polytechnic of North London School of Library and Information Studies had no such thing as an institutional tie in 1983 (and what would it have portrayed? Three sociology lecturers couchant?). And if only there were a CILIP tie.
A suit in sub-fusc colours and a sober, but not too sober, tie are the best one can manage. I keep loud, newsreader-type ties for the first day in the new job, once I have been appointed. Bow-ties require even more discretion. I have occasionally worn the old school tie in the hope that one of the panel will whisper to the others in awed tones as I leave the room, 'Good God, did you see he was at St Custard's? Tell the other candidates to go away, our minds are made up'.
I have left many interviews when a candidate knowing that, even if I did not land the job, I was the best turned-out, and this, along with the knowledge that I have run eleven marathons and that the panel coudn't run for a bus, preserves my amour-propre. Note, however, that, in horse races, the horse that the stewards judge to be the best-turned out rarely wins the race.
When on the other side of the table, I have tried to maintain utter indifference to a candidate's appearance and clothes. For me, they can wear a grass-skirt so long as they're clever, creative and make me think they would be exciting to work with. But not every interviewer is as enlightened as me. And even I will dismiss a candidate who shows up wearing a Porridge Court tie. However, since the only interviews I'm invited to at the moment are the ones at the JobCentre every fortnight, my advice does not merit a great deal of attention.