Riding with yourthumbs on topkeeps your hands, wrists, elbows, shoulders in a "neutral" position, which allows your joints to move most freely for an elastic rein connection.
A strong back is necessary for the horse to be able to achieve and maintain self carriage and collection for any length of time under a rider. Asking for too much too soon can cause your horse to resent his work.
"So what do we see when we watch these masters at work? We learn what it means to become a good rider. It means to be picky, detail-oriented, motivated for your whole life, paying attention to every stride, having a system but with the flexibility to adjust it. Even before you can control the horse, you have to first control yourself (99 percent of problems with a horse are caused by the rider). Finally, a good rider needs the willingness to say, 'I made the mistake. The horse didn't make the mistake.'" ~ Christoph Hess
Make sure the horse can travel in a balanced way on a circle in trot and canter BEFORE the added challenge of a rider (with good lunge work.) Then when the rider gets on, they can improve things from there.
"There is no miracle, there is no magic wand. It is just education, trying to be as clear to the horses as you can. When I give an aid, is the horse going to understand?" ~ Emile Faurie
Too much repetitive motion has a tendency to inhibit muscle symmetry. Always aim to mix things up in your training (whether horse or human), so that you can develop balanced musculature.
"A horse's energies are gathered up from behind and by yielding on the reins and giving him the room to step through to the center of gravity, the neck will shape to reflect the activities in the haunches. Trying to achieve collection by working on the horse's neck cuts the horse off in the front, confining him and preventing the hind legs from lifting, suspending and powerfully supporting the rider's balance." ~ Charles de Kunffy
"The legs bring the horse to the seat, and the seat brings the horse to the hands. When the teacher says 'shorten the reins' it needs to be translated into: 'engage the hind legs, sit on them, and then take the slack out of the reins', because if you shorten the reins from front to back, the horse will only resist." ~ Thomas Ritter
Rather than simply holding in a combination or when riding down a line of jumps, individual half halts performed in time with the horse's stride will be more effective.
What do we want from our horses over fences? Consistency and balance. If we as riders are more consistent and balanced with our own position as we ride a course, we make achieving that with the horse much easier.
"A significant portion of the art of dressage lies in your ability to differentiate between the positive tension of focused athletic effort, and the negative tension of resistance, fear, and anxiety." ~ Katherine Bateson Chandler
Horses that are truly moving with a relaxed and happily swinging back will not give you a feel of a "locked jaw" in your hands. Any resistance that you feel in your hand while riding ALWAYS starts in the horse's back.
When a horse is equally laterally supple in both directions, it will be evident in the ease of which you are able to perform changes of bend and direction.
Too much repetitive motion (of any one thing... trotting, cantering, circling, hills, jumping, leg yielding, etc) can easily cause fatigue, soreness, boredom, or a sour attitude. It is best to mix things up in your training.
"When introducing new questions make sure they are fair, but don’t over prepare the horse. Let him find out it’s an oxer/filler/bounce when he gets there. They need to learn to react and make quick decisions." ~ Eric Smiley
"All riders need very loose joints - loose hips, loose shoulders, loose elbows, loose knees, loose ankles. When I say loose I don’t mean uncontrollably loose, but they need to have a very good range of motion, and an absence of unwanted tension. A lot of riders when they are not comfortable in forward seat tend to grip with their knees, and tend to have a little stiffness in their ankles." ~ Tad Coffin
Both horses and riders ultimately learn from and cement behaviors through repetition. This is why you need to make sure that you are repeating things CORRECTLY.
Maintain your good score for your trot or canter lengthenings by performing a clear, precise, and active transition back to the working gait at the end of the lengthening.
Many times riders ride each stride to a jump, but then sort of "freeze" right when they get there. Usually this is because of nerves, or because the rider is worried about trying to make some preconceived takeoff spot happen.
Make sure you ride each stride, including the takeoff, and even over and across the jump if necessary. Don't "jump ship" and leave your horse feeling alone right when he needs you most.
If you want to develop a nicely shaped crest (the top of the neck muscling) on your horse, you have to make sure your horse is truly seeking the connection - reaching into the bit, rather than backing away from it.
"Since the criteria of a correct seat are the same as the criteria of good posture in general, being constantly attentive to one’s bearing when standing or walking is excellent training. A correct vertical posture of the head and the trunk on horseback is not a special posture applicable only to riding." ~ Kurt Albrecht
If you do all of your training on the exact same kind of footing, (i.e. either all firm ground, or all sand), you might be putting your horse at an increased risk of possible injury. Training on a variety of different surfaces will develop both the strength and the elasticity of tendons and ligaments, which will help to prevent injury.
"It’s important that the rider doesn’t disturb the horse – leaning this way or that – and that is the same with this pulling and pushing. You give a half halt, but half halt is not just pull back and then let go. First of all you have to push the horse into your contact, and while you do a half halt, the horse should not get tighter in the neck and not get slower in the hind legs. Actually we want to engage the hind legs. It’s something you have to work on all the time, and get to feel it. When you tell the rider, now this, now that, you are already too late. You have to practice this, so that the riders get to feel it themselves." ~ Monica Theodorescu
The half pass helps to develop the brilliance of the extended trot, by increasing hip and stifle flexibility and range of motion, and freeing up the horse's shoulders.
True lightness does not come from playing with the bit until the horse feels lighter in your hand. Only real hind leg engagement and lowering of the quarters will bring about the true lightness that you are looking for.
"You are connected with your seat to the horse’s back, connected with your legs to the horse’s body, and connection can only work if it goes through the whole horse and into the rider’s body, and from the rider’s body back to the whole horse." ~ Susanne Miesner