I have to think that you start by handling the incident as you would any other vehicular accident. Most of the prior responses seem to be in line with that approach. For example, I would encourage accident victims to stay put and not move them myself, unless conditions dictated that not moving them put them in great danger. If either a car or plane was on fire, you might consider moving the people insdie or near it. The materials that might be burning in either a car or plane should be similar. The plane is likely to have things that burn differently than those in a car, the fuel may burn differently, but it's still going to have the same type of fires, with probably most commencing with Class B materials.

First thing, get help coming. Have someone make a 911 call and know it's being made.

Second, begin to assess things. What happened? What is still happening? What position and condition is the vehicle in, and does that position and condition pose a threat to anyone in it or around it? Can you change that position and/or condition to improve things? What are the conditions of people involved, and do any of them need attenion right now, such that if they do not get it, they are not going to make it? If they are in danger, can you do anything about it? Is there more than one person in such a condition? Which one needs more attention, which conditions can you address? How far out is help? When are they expected to get there?