I've outlined a general 'curriculum' below starting with a beginner and progressing to an intermediate level, realizing of course that many will already have riding skills and will progress faster through the first steps.
Ground safety (how to safely approach, halter, lead and tie a horse)
Grooming & picking out hooves
Longing
Saddling / bridling
Mounting / dismounting
Hand / leg position
Whoa / steering
Walk
Back-up
Body control (flexing, moving the shoulders & hind quarters, sidepassing)
Jog / Trot
Lope / Canter / lead recognition
Instruction as to anatomy and conformation, hoof care, nutrition, health care & husbandry, correct wording and nomenclature will be mixed in with lessons so that students learn in a 'hands-on', easier to remember manner.
Once the above 'steps' have been mastered correctly students will be ready to advance on to their main area of interest. Listed here are details specific (but not limited) to certain disciplines (in no particular order).
While lesson-level horses (meaning they can perform the maneuvers well enough to teach a rider, but not necessarily at a level to compete and win on) can still be supplied, it is strongly recommended you have a personal horse to advance on.