I am going to answer your question more about the "seat" type used for equitation. First of all, there are four main seat types (half seat, light seat, full seat, and driving seat). Any and all of these seat can and should be used in the class if the time is appropriate. Though you may see quite a few riders ride their eq rounds with a full seat, most judges (and top trainers) agree that they prefer to see riders in a light, sometimes half seat, using the full seat when necessary. Below is an article that will go a little more in depth if you want to check it out!
Actually half seating is for the hunter classes since it helps your horse move better. I usually sit the canter in my eq flat classes and the sit the trot before you canter your course.
Appearance will always make a good first impression (clean boots and a well fitted hunt coat) it can help show off your eq plus it will make you seem more professional😋 Also try to ride in a half seat position since it's the preferred style in eq