The most important thing that was ever said to me was "The moment you have to do a forced landing the insurance company owns the plane".
That was an astounding revelation.
Before my accident thought process was "how do I save the plane". Afterwards it became "how do I save the people in the plane".
Gunny is right on with always running "what if" in your head.
Aside from that, the best pre-accident preparation is learning, learning, learning, learning. Never stop learning. Some of this will be with an instructor, but most will be by yourself. Most pilots have absolutely no idea what their plane is capable of, nor how to fly it properly. You can see/hear this everyday just by watching guys land. High or hot, landing long, while bouncing down the runway. Once they have their license they think "I can fly a plane now" and quit learning. In reality they become worse pilots as time goes on, they become complacent, and bad habits set in.
And don't be cheap. Especially when it comes to your engine. Aircraft engines are crap to begin with (blame the FAA and lawyers for this), there is no reason to worsen the situation by having someone overhaul them who does not have a sanitized work area nor the proper testing/measuring equipment (and might be buying the cheapest parts they can find). Hell, in a former life I was one of the top auto mechanics in the country, asked to mechanic for the Lotus Formula One team and there is no way I'm overhauling any of my airplane engines, nor even changing out a jug (under the watchful eye of an A&P IA of course). When that time comes the engine will go to one of the top engine builders.
Airplane owners (in general) are so cheap that it takes a long time (as in many months) for me to train my mechanics that their primary responsibility, EVERY TIME they work/look at my plane, is to find stuff to fix or needs replacing. They are used to being asked to do repairs as cheaply as possible, or not at all. This came about from doing all the upgrade work on the 185 and in the process seeing how much stuff was done incorrectly, was worn out, or already not working properly.
[sorry for the rant]
Oh, and when it comes time for an annual or conditional, do an owner assisted one so you learn what your airplane parts are supposed to look like, and what needs to be checked. And when you clean your plane, use this time to look everything over carefully, such as are the VG's all still in place, are the flying wires taught, is there enough nitrogen in the tires, how do the brake pads look, are any bolts, nuts, or screws coming loose, are there any smoking rivets, etc, etc. If you have someone else clean your plane teach them what to look out for. You can't have too many eyes looking things over.
Learn and maintain. The best pre-accident preparation in my opinion.