ASsuming you've given your horse a bath and they are braided and trimmed etc etc, then keeping them inside a stall is the next best thing. Throw jammies on that cover the the head and neck to protect the braids and keep the horse clean, a cooler and wrap them up over night. The legs are easy to quickly brush off in the morning unless you own a grey then you are always at risk of having your horse covered in green regardless of how hard you try to keep'im clean.
Show sheen is alway a great product to put on the prior to a show as it helps decrease the chance of poo or various other things to stick on. hmmmm....I think thats it for now.