1) Don’t Fly Junk! By this, I mean that if you find that the Owner/Operator of said aircraft seems to have either a cavalier attitude about maintenance 
2) Your time is valuable. Don’t ‘give it away.’ Flight Instruction is worth whatever you charge & ground Instruction is too. Establish that early on. Ergo, if you charge $50/Hr & have a typical 2 Hr block booked & WX precludes you getting ‘air time’ with your Student, have a 2 Hr Ground Session instead & it is not a ‘Loss’ for either of you.
3) Don’t be timid about establishing your PIC authority; when you say, “I have the Controls!” or “My Aircraft!” your Student’s feet & hands must IMMEDIATELY come off the controls. This needs to be established before you ever set foot in the plane. Accept No ARGUMENTS here‼️ A lot of these students today are well-heeled execs, Business Owners, Doctors, Lawyers, etc. and some have a tendency to regard you as their “inferior” as if you are merely a Doorman, Barista, or Valet. Squelch that Attitude politely but firmly very early on, or it can become a Nightmare for you. Any trouble with a prospect who prefers to take his/her Grandiose Delusions into the air with you…’cut them loose’ to go find someone else to fly with & ‘Don’t let the door hit ‘em’ in the ass on the way out.
5) DO NOT discuss Politics. Half your Students will be ‘on the other side’ – in some places that will be more like 80 or 90%. Too bad. Not your problem. Just be yourself & don’t get drawn into the ‘Vortex’ where there are No Winners.
6) Your first Student to ‘Solo’ will be ready before you are‼️😅 No problem. It’s pretty much true with all of us… that ‘second-guessing’ & thinking 🤔 💭 ‘Did I cover EVERYTHING?!’ Don’t worry about it. In time & with greater Experience you will know when the Student finally ‘clicks’ & clearly is ready for ‘three times around the patch!’ Just be aware that in the beginning, you will feel pretty anguished standing there on the sidelines watching your fledgling out there on his/her own for the first time. Make sure to ‘Celebrate’ afterward! This is a ‘Big Deal!’ for all concerned‼️
8) Don’t be too eager to ‘jump on the controls’ (or the radio) with every deviation from ‘perfection.’ You weren’t perfect either when you were starting out. Try to just get them to be aware of things they can do to help themselves, instead, like say releasing that ‘Death Grip’ on the yoke & holding it instead like a Stradivarius violin 🎻 or a beautiful romantic partner. Use some gentle humor in the cockpit to de-stress the situation. Leave them room to discover, learn, and grow.
9) Beware ‘Experienced Pilots’ who need a Flight Review or who are ‘Rusty’ They will surprise you with Totally Mondo Bizarro behaviors and techniques that defy any expectation! (Pilots get weird with added hours and no dual…)
10) NEVER become Complacent in the Cockpit! It can kill you.
(Send us your list of “10 Rules” you live by as a CFI…we might publish it!)