From what I've heard, the only real suprise sudden engine out on a piston is fuel related - or lack there of: no fuel = no fire = pooooof - no engine; and Carb icing is the other. Here the only indication is if you are keeping level flight, you'll either be slowing down or pulling more collective to keep up...the governor masks it quite well untill = poooof....
As TC said, car engines generally don't die so sudden. They get that rough sound/feel to it before they die. If you are flying only one or two machines, get to know them. Power checks and monitoring their norms will give you a warning for when it starts to go pear shaped, which hopefully you can get repaired will in advance.... and keep the machine clean. Nothing worse than using a dirty machine that someone doesn't give a hoot about. As soon as a leak appears, you'll spot it and get it seen to. I have flown a few dodgy and seen some frightning machines.....
Best advise other than that.............know your emergencies, and I'm not talking just about the auto - so many don't know what to do when a warning light comes on and end up wrapping a tree for nothing...!