G-SPOT, hi, welcome to the brotherhood! Best advice I can give (after about 1500 hours instructing, up to CAP509 eventually) is:
THE STUDENT MOST LIKELY TO KILL YOU IS YOUR BEST STUDENT!
My first summer instructing, I had a student who had excellent handling skills, worked very hard indeed (every day off, he was at the club, if the weather was bad he did groundschool). He ended up finishing his PPL in 43 hours (excellent for a part time course, spread over 4 months of Scottish "summer").
Just before his GFT, I asked him to do a glide approach. I was happy, because in general his flying was almost up to BCPL standard. I did not allow for the fact that his EXPERIENCE was nowhere near that of a BCPL candidate. In slightly windier conditions than he had practiced glides in, he lost a little speed (only 2 or 3 knots), I didn't catch it, and we did a very hard landing. The engineers checked the a/c out, the CFI gave me a chewing out (which I did not pass on to the stude; it was my fault), and we both learned about flying from that!
PPL checkouts can be even more dicey. Few PPLs get enough flying time to be really current, and my skills certainly deteriorated between checks (until I got my AFI rating, and could fly regularly with other people paying!) Watch them like a hawk, keep your own lookout, and if you adopt a relaxed seating position during the flight, go back to full "alert" posture as you enter the circuit. If nothing else, the sight of you resuming a "ready to take control" seating position will remind th student not to relax, even if he is almost home.
I was lucky, I survived being a prat- I haven't made that particular mistake again. I have lots of imagination- I can always think up new mistakes to make!
