Another thing that separates a professional from an amateurish show ring performance is the way the lines in the course are ridden. We've all observed the consequences when a rider jumps in to a line from a tight distance or a long distance, with lack of impulsion, or with "too much horse". But a less-than-ideal "in" doesn't mean you can't have a nice "out." They key is to know what to do inside the line.
You can't right a wrong until you know what "right" is. A good first step is to learn what a 12-foot stride feels like on your horse. You can practice this by riding ground rails. Have your trainer help you correctly space ground rails to create a five-stride "line" that you can canter through. If your horse's natural stride is longer than 12 feet, you may be required to sit up and steady him. If it's shorter than 12 feet, you may have to send him forward. You want to find the "lick" that lets you flow through in five easy, even strides. (Ultimately, that's the pace you'll want to carry from the moment you pick up the canter to begin any course - so knowing exactly how to create it is critical.)
Knowing how to adjust when you don't jump in to the line exactly out of stride is your next assignment. If you get a tight distance going in, or if your horse jumps in too boldly, it's going to affect how your horse covers the distance to the "out."
Continue practicing with your five-stride ground rail line. Pick up the canter, allowing plenty of time to establish that 12-foot "lick" (don't make the all-too-common mistake of starting the exercise before you've created the balance, engagement and length of stride you need). If you hit the first rail right out of stride, good for you. You can flow through the line maintaining your pace. But if you don't hit the first rail precisely...it's time to initiate Plan B.
The most common mistake riders make when they get in to a line wrong is to not make the appropriate adjustment soon enough. They jump in too big, wait a few strides and then realize "oops, I need to wait." They're still hauling on the horse at the next fence. Or, they jump in weak and do nothing for a few strides. They realize they need more step and panic and gun the horse forward, most likely resulting in one of those fences that makes people gasp and cover their eyes.
Whatever adjustment you need to make, you need to make it within the first few strides upon landing. Or sooner! Look early, think ahead and ride proactively. Be aware of the step you're on and how it looks like you're going to meet the "in" of the line. You see a long one coming, sit up and prepare to do a shorter release. Stay a little taller, land already collecting the stride. For a tight distance in, balance up, keep that leg on all the way over the fence and land in your two-point, pedaling the bicycle! Your goal is to make the correction promptly enough so that you can re-group and ride the "out" with a steady stride and a soft, balanced horse.
Lines aren't always set precisely to the 12-foot stride standard, so you'll need to practice all of the above on lines of varying length. When you can reliably ride the lines and make adjustments on the 12-foot stride, set the line a little long, and then a little short, and practice, practice, practice. If you have a long line and jump in weak, the amount of leg you need to move up and cover the distance may surprise you. Likewise, collecting the stride after jumping too strongly into a short line will require extra effort!
Practicing at home is only part of the equation. The savvy competitor plans his ride long before he gets on his horse at the show. He has read the course diagram and knows if the lines are set long or short. But he understands that just knowing the length of the lines isn't enough - a long line going away from the gate at the beginning of one course is going to ride differently than the same line if it's coming toward the gate at the end of a course. He's watched horses in classes before him go to see where to turn for the best approach out of every corner. If possible, he's walked all the way around the arena on foot to see just how shallow or deeply a diagonal line is set (you don't get the whole picture from a single point of reference at the in-gate). He's aware of whether there is an uphill / downhill aspect to the arena, and how that will affect his plan to ride to any given line. And during his warm-up he assesses the energy level of his mount - which may vary markedly between day one and day four of the horse show. All these variables play in to his strategy.
There's a lot more to it than merely memorizing the order of the fences before you go into the ring for your round. Even the simplest of hunter courses involve strategy. Of course, if all you want to do is show up at the in-gate and hop on your expensive, professionally schooled-and-tuned mount and have your trainer recite the course to you - that's your choice. Just don't be surprised when a rider with a less-fancy horse, who has put the effort into upping his or her game, snatches that blue ribbon right out from under your $350-breeches-clad backside.
I'm just sayin'.