Excerpt:
Beginning English Rider's Companion
Straight from the horse's mouth

Watch a few lessons at the candidate barns. Here's what to look for:
Patience with students, especially beginners. (As noted earlier, some experienced instructors feel diminished by teaching beginners. However, those who understand the sport--and their own business!--will welcome them. Not only are they the future, if they are started right, they will be a joy to teach and to watch, rather than a frustrating re-training exercise.)
Absence of negative or denigrating instructions or comments to students; no matter what mistake a student makes, an instructor should NEVER berate a student.
Happy faces.
Respectful interaction between instructor and students.
Reasonable accommodation for parents to observe classes...but check, too, to see that parents are not allowed to interfere.
For adult beginner classes, check to see that the instructor does not talk down to the students.
Although it will be difficult, assess whether all or most of the students display improved skills between the beginning and end of the class; failing that, talk with them and see how they feel about what they are learning. Or, take a knowledgeable friend with you who can visually assess the progress in the classes.
Ask for a barn tour, and observe well.

Are the aisles clean? Realize that clean in a barn isn't the same as clean in a house. There will be some dirt from recently picked hooves, and a few wisps of hay and so on. What you shouldn't see is a pile of trash in the aisle, more than one pile of 'road apples' in any horse's stall, wet and stinky stalls, dirty saddles and bridles laying around and so on.

Riding theory and philosophy

Xenophon, a 4th Century B.C. Greek soldier/philosopher, claimed that riding "makes the body healthy, improves the sight and hearing, and keeps men from growing old."
Winston Churchill, the leonine Prime Minister of Great Britain during World War II, took all that to a psychological level. Said he, "There is something about the outside of a horse that is good for the inside of a man." He also admonished wealthy men not to give their sons money, but horses. Money would make a lazy fool of a boy, while horses would demand the boy's attention and engagement.

And then there was comedian Joe E. Louis. He said, "You can lead a horse to water, but if you can teach him to roll over and float on his back, then you got something."

These three quotations could almost be a 'which one doesn't fit' exercise. But the fact is, they all say the same thing: The horse, exactly as it is now and has always been, is a fundamental asset to mankind.
Riding is exercise, as Xenophon said, and, moreover, it is exercise that demands much of the muscles, the eyes--everything. And so, it keeps everything tuned up.
Churchill made the point that getting away for a ride is good for the mind and spirit, a mini-respite from whatever else is going on in one's life. And it might also be construed to mean that, in view of the horse's great strength and speed, man may properly be humbled at the same time as he is exalted for being allowed among all creatures to sit upon the horse.