So, leave all seat belts on until the airplane has come to a stop, even if it starts to fill with water. Once the motion has stopped, with your belt still on, reach over and open the door, which you should be able to do without looking. You might have to wait until the cabin fills with water. Don't let that panic you, even if the airplane is sinking and it's getting dark outside. Just wait until the last second and take a deep breath. Then get a good grip on some predesignated close-by handhold and "walk" your way to the exit, being sure to keep your feet planted on the floor, one step at a time. Plan ahead exactly where you will place your hands and your feet as you make your way to the exit. This can be a real challenge in a neutral buoyancy environment, so you need to make it a conscious effort. Never try to swim your way to the door; tell your passengers the same thing. If the nose is down, you'll end up in the back seat. If the tail is pointing down, you'll end up stuck under the panel. You have to hang onto something and hoof it, even if it's upside down.