The evenness of the contact reveals the straightness of the horse. Instead of being tempted to try to fix unevenness in the contact with your hands, focus on helping your horse to use both of his hind legs evenly.
Think about having weighted elbows. When your elbows are hanging down by your hip bones because you have relaxed your shoulders and are allowing your elbows to drop, your hands will be in the right place.
Do not miss the possible opportunity to shorten your reins when your horse changes his balance in the direction of increased collection. But make sure you maintain forward feeling hands when doing so.
If you do miss it, and are riding with a length of rein that was more appropriate to the longer, lower frame that you had previously... you risk losing the amount of increased collection that you had just attained.
If you ask for too much angle in any lateral movement (more than your horse can handle at that moment), you risk impeding the balance and fluidity of the movement, which should be some of your top priorities.
The inside rein is like the directional or turn signal in your car. You use it to indicate the direction that you plan to go, but it doesn’t actually turn your car.
"I like to think about making my body longer in the front to make me sit up instead of thinking ‘shoulders back,’ which can make you stiff." ~ Mary King
If your horse leans in heavy on the inside shoulder, or falls out through the outside shoulder on the circle in both directions, chances are it is something that YOU are doing as a rider that is the cause of the problem.
When you halt and salute the judge at a competition, remember to smile! This will send the judge the message that you are confident about your performance, which can impress the judge and may even influence your scores in a subconscious way.
It can be tempting to want to repeat something over and over when you feel like you are making some progress on a movement you have been struggling with.
But it will be more productive to reward one especially good effort... give the horse a break, and move on to something else instead. When you come back to that exercise, your horse will remember what you did.
When giving the aid to canter, let your outside leg sink down and back as the last part of your canter aid. If you lift your leg up and back to use it (as so many incorrectly do), you will end up losing your seat to some degree, and may also end up sitting crooked.
"Contact has to be just that, contact. People think 'oh this horse is very light I have nothing in my hand' – this is wrong because then you have no contact to his hind legs." ~ Jean Bemelmans
Posting or rising at the trot can sometimes be a useful exercise as you ride a collected trot. It can encourage the horse to think more forward and swing more fully through the body.
You must keep riding forward into the bit while riding your horse in a stretching position. A low neck does nothing without the horse remaining active and swinging behind the saddle.
"There are two types of seat, active and passive. Don’t ride hard all the time: active, passive, active. The main thing is to think about the horse’s back a lot." ~ Carl Hester
Train your horse to understand that he should stay at whatever speed you put him in until told otherwise. Remember that every time you allow your horse to make a decision about his speed or energy level (or don't realize that he has done so), you are training him to make these decisions on his own.
"The horse has to have independence, responsibility, and tolerance for a variety of distances [when jumping] because you’re going to mess up and the horse has to be able to cope." ~ William Fox Pitt
"Make him proudly independent of you so that he understands his job so well you merely walk the course and then show him the way. Tell your horse what you want him to do, and then allow him to do it." ~ Jimmy Wofford
"If you put a muscle where it doesn’t want to be, it is broken down – not build up."
So don't go thinking that you are building the right muscles when you force a horse's head into a position. The horse has to be using those muscles correctly to actually develop properly.
Don't "sort of" have a contact. Try to either ride with a connection, or ride with a loose rein. That "in between" area where there is sometimes a feel and sometimes not, is where horses learn to fear and/or evade the contact.
"But for the horse, riding is indistinguishable from training; you're training your horse every time you ride it, like it or not." ~ William Steinkraus
Don't let your horse lean on your leg in the ribcage area. Teach him to yield to that pressure. Swinging the quarters out in response to your leg is an evasion, and is a very different response than truly yielding and bending in the body.
"The word Dressage is used precisely because of its double connotation for taming and training. One cannot train any animal without having its full attention and focus on the trainer. Taming—focusing the horse’s attention— is difficult because he is genetically determined by instinct and is programmed for multitasking. The rider’s job is to gradually replace the horse’s instinctive behavior with one of utter focus on his rider. This enormous change in the horse’s behavior— disconnecting from his instincts and focusing instead on his rider—can be earned only by a rider deserving of the horse’s total trust." ~ Charles de Kunffy
When a horse collects, his shoulders will come up naturally as he engages and lowers his croup. Do NOT attempt to artificially raise the front end. That would be front to back riding, which is incorrect.
Always keep your eyes up when you are walking your course. See exactly what your horse will be seeing for the first time while under pressure, and think about how he might react.
"You can't teach someone to ride cross-country in one field, or even with constant instruction. It has to become a natural thing, and the only way to achieve that is to get out and do it." ~ Bruce Davidson
When you first begin to work on movements like shoulder in and haunches in, always start out with minimal angle and focus more on the quality of the bend.
Eventers need a saddle for cross country that allows them to move their center of gravity back for drop fences or anything on a downhill slope. Make sure your saddle has enough room for this to happen.
To be truly safe when jumping cross country, both horse and rider should learn to love that deep takeoff spot.
Please note that a "chip" is not the same as a deep spot. A chip is when the horse adds a stride unexpectedly, usually because the rider is going for a long spot or otherwise interfering with the horse's striding, and the horse is out of balance. And that's where the rotational falls happen. A deep spot in balance is the safest place to be.
For the cross country phase of Eventing, we need to be able to keep our horses balanced at the gallop while riding over rolling, undulating terrain. Yet it is becoming quite common these days for horses and riders to do most or even all of their jump training in a flat, perfectly manicured arena.
Make sure you do enough galloping and jumping training out on rolling hills if at all possible, to become adept at keeping your horse balanced at the gallop with the added challenge of varying terrain.