I'm not sure what kinds of tips you're looking for but I'll give you some simple tips that competitors often forget.

Showmanship: Make sure your horse is clean! Clean inside your horse's nostrils and ears, under the tail, around and in between the udders if you have a mare and around the sheath if you have a gelding. Scrub out any stains under the horse's barrel, in between the front legs, and chest. And make sure your horse is clipped thoroughly around the edges of the ears, all around the muzzle, the lower legs especially around the coronary band, and clip off the long whiskers around the eyes, but leave the eyelashes alone! These are areas a lot of people forget about and that can cost you a ribbon. You can also make your horse look extra sharp with some show sheen (but avoid the saddle area if you plan to ride later), some clear hoof polish, and some face glo. If you're going western, make sure your horse is banded and if you're English make sure your horse is braided in tight, neat braids. You can use human hair spray to tame fly aways! And don't forget about your own appearance! Keep a lint roller on hand. Wear only a clean show outfit. Make sure everything fits and that your boots are polished. Pull your hair back neatly and secure all fly aways with hair spray and bobby pins. Apply a small amount of make up. You want to use enough make up to look presentable but not so much that you look like a clown. You can gain a lot of points in showmanship just by being well turned out. The class is based heavily on grooming, so don't lose points there. It's easy to get a perfect score in the grooming portion of the class by paying close attention to detail and putting in the prep time before your class.

As far as the pattern goes, it's a good idea to spend time practicing stop to trot and trot to stop transitions, pivots and walk arounds each time you work with your horse. It doesn't take much. Just do ten minutes of showmanship practice before each ride and you'll find you and your horse can nail a crisper, more practiced pattern at each show. Pay close attention to the pattern at the show. Note what side of the cones you're supposed to be on and things like that because it's often those little mistakes that get competitors knocked down in the placings. And even if your pattern isn't perfect, you can sometimes make up for it with how you present yourself. Smile! Have energy! Look like you're happy to be there! Make your transitions smooth. Don't hesitate! Keep your chin up and don't be afraid to look the judge in the eye! And as you're returning to the line up or exiting the arena after your pattern, always glance over your shoulder at the judge one last time.

Trail: The best advice I can give you for trail is to take your time! Remember that trail class is not a race. You can take all day to do that pattern if you want to, and I found that I encountered more trouble with a trail class when I rushed. My horse would get flustered and trip over things knock into things, or overshoot things, or when I rode my mom's mare, she would get pissy and not listen, ring her tail and threaten to buck. Talk to your horse. Do everything one step at a time and relax. It also helps to practice certain skills at home. It's way convenient if your horse knows how to neck rein. All my horses know how to neck rein, even the ones who ride strictly English. It's good to practice low level dressage movements such as side passes, and extension and collection exercises. This gets the horse moving off your leg and gives you more control over your horse's gaits. You should also practice backing patterns. This is a good test of patience and control for horse and rider. And you can practice common things you see in trail classes, such as getting the mail, walking over tarps and bridges, and opening and closing gates. If you don't have this equipment available, a plank of plywood works for a bridge and two jump standards with a lead rope looped over the tops works as a makeshift gate.

Hunter Under Saddle: My greatest advice for placing in hunter under saddle is consistency. Find one consistent pace and stick with it. It's also a good idea to stay on the rail. Most of the time, the nutty horses careening around the judge on the inside track place last. You should also do your best to groom yourself and your horse as if you were entering a showmanship class. Hunter judges like a well-presented pair. So even if your horse's head set isn't perfect, or if his transitions are a little rough... whatever your weakness might be, you can often save face by keeping it steady and on the rail because that's where a lot of other people have trouble.

Those are the three classes I have the most experience in and feel most qualified to answer. I hope I could be of some use to you! xD