I find the easiest mistake is to leave carb heat on for landing,
I've caught myself a couple of times on doing the after-landing check to see I've left it on.
I don't suppose it is the worst thing to happen and know there is another topic about carb heat and this gets a mention.
I think I am getting better as I don't think I've done it recently!
Re high speed approaches etc in a training plane.
I am a mere low hours learner but have several pals with many years commercial,military and private flying.
They don't p*ss about like that!
Lister