I don't wear a tie (but I am female). When it is cold I wear a scarf instead. White shirt and dark trousers and a dark jersey seem appropriate to me for most instructors. NO gold bars! However, I do take exception with this current fashion not to wear a belt on your trousers, which makes them hang underneath the paunch or off the back of your rear end, exposing your underpants. It looks so childish and scruffy and I cannot take anyone seriously who does not use a belt if there are belt loops in the trousers. It is just like leaving the laces out of your shoes...which should of course be leather and polished, not those clumpy huge plastic ones.