Lots of good advice up there. Here's something that has not been covered yet:
Once you've rolled over, don't screw around taking pictures and laughing and carrying on. Try to get the thing back onto it's tires ASAP. The longer it's on its side or roof, the more your vital fluids are going to migrate. Anything that has fluid in it (axles, t-case, tranny, engine, power steering, fuel tank, radiator, etc...) could be draining itself. You may not even realize they are draining, as the fluid could pool somewhere in the seedy underbelly of your rig and you could drive off without knowing that it is empty. Also, all that fluid that does spill will end up on the ground. The longer your rig is tipped the more likely your engine will be hydrolocked when you get it back upright too. This brings up another point:
Once it is back upright, don't just try to fire the engine right up! First, very briefly "bump" the starter and listen if it sounds like the engine is spinning freely. If it sounds normal hit the starter again for just a little bit longer. If that sounds normal go ahead and try to start it up. If the starter turns slowly, stops, or sounds like it's working harder, stop and pull out your spark plugs. If your engine is hydrolocked (meaning the oil from the crankcase has drained into the cylinders) and you try to start it, you could end up sending a rod through the side of the block and buying a new engine.