Assuming it is a light aircraft you would follow the same procedures as any vehicle crash.

One thing I have noticed with plane crashes you tend to get the two extremes either light injures or everyone's dead there is not much in between. Helios are of course an exception.

One thing to watch for is if it's a high wing aircraft the fuel tanks are in the wing, most of the time a real tank not a wet wing, the fuel is gravity fed to the fuel pump and engine. On most Cessna products there is a fuel sector in the middle of the front of the instrument panel, do not bother with it the push rods the work the valves tend to bend making to useless. If it is a low wing many of then only have one door on the right side of the cabin and the fuel is in the wing several company use a wet wing where the skin of the wing is the fuel tank.

The master switch is usually a rocker switch on the lower part of the panel just to the left of the engine controls (not always but most of them seem to do this) If it is a low wing many of then only have one door on the right side of the cabin and the fuel is in the wing several company use a wet wing where the skin of the wing is the fuel tank. Also the master switch does not turn the ELT off. Do not bother with the key switch that only works the mags that will not have power as long as noone moves the prop.

Please note any action you take and report it to the NTSB or the state investigaters when you can.