Turn on the forehand and leg yield can be used to teach the horse that the rider's leg can mean something other than, "Go forward." The horse must understand this concept in these very basic movements before you will find much success with any of the more complicated lateral movements.
Thinking about steering your horse from the middle of his body rather than his nose will help you to keep all of his body parts under control.
When schooling a green horse through any complex where the last element is a tricky jump (skinny, angle, corner, etc), it is smart, if possible, to school the last element first. This will set you up for success as you then jump through the whole complex, as your horse will
"When you relax your arms and feel the reins softly you need to feel that your horse wants to step into the contact. If you do not then he is behind your leg and seat." ~ Yvonne Barteau
Studying riding theory will make you a better rider or trainer in many ways. Trainers need a knowledge base broad enough to enable them to apply the appropriate system for each horse/rider combination in front of them. Riders need to thoroughly understand what they are trying to do and