Put your jack under the strongest looking steel frame part you can locate and think about around 2000 lbs being held up at that point. Stay away from floor pans, and any broad metal plates. Also, think about the fact that the suspension carries the weight of the car.. as long as it doesn't compress and you can find a level spot, you can jack up by the suspension arm.
The advantage of that point is that its a heck of a lot faster if all you're doing is changing a tire as you don't have to lift the body way up to get the wheel off the ground.
But above all, use your brain and consider what 3800 lbs of car would do to you if it fell on you!