In the JTR classes at higher levels shiny, loud coats are in. At the A and smaller regional shows I see alot of tan/lighter jackets, or dark jackets with loud shirts.
As far as tips, try to be steady, most judges really want that in the JTR classes. Taking lessons, and watching other hunter classes are the best way to learn what you need to know. nothing beats experience

And make sure you show in equipment that is good for your horse, not just what's trendy