Does it have EQ or the word "Pleasure" attached to it anywhere? If it's a pleasure class (bar in mind this can vary from area or area) but around here judges look for a slightly longer rein and they want your horse to be consistant going in both directions of the arena. A lot of judges will also look for big floaty movement. In an EQ class our judges like a little more contact on the reins, heels down, flat back, hands NOT in your lap and looking up. They will look for a riders who position doesn't change from gait to gait. However you need to remember that the judges where you live might not look for the same thing the judges look for around here. Also we do hw on our judges and if the judge has a big hunter/jumper back around you will want to be tiped slightly in front of the vertical in your eq class and almost in a 2-point or 1/2 seat while cantering. Where as an APHA judge will want you up-right with a longer rein. Sorry if this doesn't help but I know that's how things go in our area.
I think the key thing that judges look for is CONSISTENCY.
As a pleasure horse, the judge needs to see the same picture every time he looks at your horse. The speed needs to stay the same, the horse needs to stay in the same frame and have the same pleasant expression. Anytime your horse breaks away from that consistency - raises his head, speeds up down the rail, breaks gait, gets annoyed with other horses close by - you sink lower and lower in the placings.
As an equitation/horsemanship rider, the judge is looking for your position to remain consistent and balanced throughout your ride. Do your legs flop around? Are your hands high one minute, low the next? Do you lean forward too much at the different gaits? Are your eyes ALWAYS looking up, where you are going?
If it's equitation it's judged on how you ride... so if your horse spazzes or a situation arises - how do you handle it? I rode a hormonal mare once and placed 2nd in the equitation class because I had to handle the situations she gave me.