Hi,
Here are some articles that you mind find helpful...
http://www.equinechronicle.com/Features/Fromm/fromm_105.html... here's a quote from this one
'The judges were all in agreement on the following:
1) Your clothes need to fit
2) Make sure that your showmanship pants are long enough
3) Absolutely no crepe-soled boots in showmanship or halter
4) Hats need to be clean and well-shaped
5) Rhinestone belts that draw attention to your middle are a no-no in horsemanship.'
http://www.hobbyhorseinc.com/06_dress_for_success/what_to_wear/what_to_wear_main.shtmlhttp://www.hobbyhorseinc.com/06_dress_for_success/head_to_toe/head_to_toe_main.shtmlYou could also look at the show photographers site to see what people wear and how they turn their horses out../www.nrhphotography.co.uk/thumb.aspx?eventid=77
Hope that helps with what to wear.
Best thing to do if you can is go to some shows beforehand to see what people are wearing and doing.