My worst student was a CPA(sorry, recent theme)
The hardest part for me was the uncertainty of hours, but honestly I did very well considering.
I didn't mind if people weren't prepared, because honestly that's more money in my pocket. Right or wrong you may ask, I am a very fair person, and if someone is not prepared, then they are paying me to make sure they are. Remember that your knowledge and skills are an asset, and are the only reason you're getting paid for this service! I don't think there was one student that would say anything negative about what and how I taught them.
Now with that being said, I hold a 100% pass rate, with an avg 65hrs for my Private students, had only 2 instrument. All this was small FBO flying, no commercial prospect students. The easiest thing for me was sending them to their check-ride, because I knew for a fact that they were well prepared and were going be ready for any normal, and abnormal situation that could happen.
As a side-note also here, be sure you are having fun with what you are doing. It rubs off in the sense of if you enjoy it, your students will too, which makes everyone's life easier. Someone having fun learns and performs much better than one that is not. Good luck