First of all, get your waivers ready-one for you personally and a 2nd one for the property owner. Make sure that only parents or legal guardians sign for minors under 18 and that they add the names of any brothers and sister who may just come to watch. Have lots of waivers on hand for other relatives who might want to watch-if they are on the property, a waiver is signed, period.
Google is a good place to find free templates for this and you can modify them to fit! Bury them in paperwork right from the first while explaining that this is a potentially dangerous sport and that everyone eventually falls off if they ride enough. Emphasizing this can go a long way towards preventing lawsuits!
Insist on (and provide if necessary) helmets for the kids and don't allow anyone to show up in tennis shoes.
If your horse is soft to cues, consider not letting the beginners use a bridle with a bit or at the very least, loose rein only and definitely keep them on the lunge line as long as it takes
for them to start "getting it". When you've been riding a long time it's easy to forget how totally overwhelming it is for beginners!
Work on the very basics only at first and explain, explain, explain. Especially with kids, repeat yourself a lot! Balance, posture, moving with the horse, leg control and position, hand control and position and definitely let them practice a lot of "Whoa" at first! It gives a new rider more confidence to know that they can successfully stop a horse if they get overwhelmed. Spend a reasonable amount of time with ground practice, grooming and explaining horse behavior but don't deny them riding time-you will end up with a bad reputation when people gossip about not being able to ride!
If you really get heavily into giving lessons (and I've been doing it for 40+ years) you will find that you get about 50 kids for every one adult. Adults seem much more willing to spend that kind of money on their children but not willing to spend it on themselves. Teaching kids and teaching adults are two totally different experiences as you will see.
With experience you learn to gauge how a particular rider will probably progress-there is no normal
, everyone is different. Some take years to learn what another may get in 6 months. Accept it yourself and help them accept it too. Casually discuss goals especially with adults so that you can tailor your method to it.
Be professional in your attitude but make sure there is some fun involved. With kids I usually give them 5 minutes at the end of every lesson for "play time". They get to ride around the arena on their own without me yelling out instructions and practice what they've learn if they want. (I am always watching carefully on the sly!!)
As far as property fees, I've never paid more than a commission of $5 per lesson to a barn owner as I have helped a lot of my lesson people buy their own horses and they ended up boarding at the properties.
And final warning... You need to be careful not to overbook your mare if the lessons really start building up. Being a lesson horse is stressful to them and they will get very tired of it and start acting out. Lesson horses always get a bad rap but there is a very good reason they got that way!