Is it a breed registry sanctioned show? If it is, find the registry's website and download their rulebook. It'll go over appropriate attire and tack :)
AMHR is: www.shetlandminiature.com
AMHA is: www.amha.org
Nope, it's just a local county fair
My mom made me a show shirt (similar to this but a different pattern https://www.etsy.com/dk-en/listing/225388366/girls-l-lime-green-westerrn-zip-show)
Black jeans or slacks
Black cowboy hat (formed and cleaned)
Green bling belt with award buckle
Hair glued to my head with hairspray.
Round earrings (similar to this https://www.etsy.com/listing/677059455/sale-set-of-4-large-horse-show-magnetic?ref=listing-shop-header-1)
That's what I did. Remember, any point you can earn is worth it. If you look neater than your competitor, that can push you into 1st in a tie breaker situation.