I always wear a dark coloured lightly patterned suit - usually dark grey. I used to only ever wear a skirt suit for interviews, but now I think a trouser suit is fine too. I wear a light coloured plain shirt and shoes that aren't too open with a matching bag. I always make sure the shoes are freshly cleaned and nail varnish freshly painted. Make up is kept light and minimal and finger nails painted in a clear or light polish.

Good luck!