LIndbergh said that you never really know how to fly untill you have taught someone else how to fly (paraphrase).
he is right
your students will put you into situations you couldn't imagine...so be ready for anything every second in the flying environment. be ready for students who do just fine and then turn into idiots.
I know one guy who checked a ppl out in a brand new cherokee archer...he rented it and flew from thed San Francisco area toward phoenix...he left late and decided to do an off airport precautionary landing because it was getting dark (oh, he had a beautiful girl with m hime)...so he landed on the desert and took off the next day.
of course, he could have flown west and held on to the light till he found an airport...or just flew at night (you are allowed to)
be ready for anything.
oh...DON"T give lessons on credit...give the lesson, GET THE MONEY as soon as you have finished the lesson.