Get your seatbelt as tight as humanly possible.
Look around and figure out which exit you will get to and how to get there. It will be very chaotic once than plane is down.
Remove any sharp objects from your body.
Moisten your shirt with any liquid available (urine if necessary) to breathe through if any smoke is present after impact.
If you didn’t in step 4, empty your bladder. This will help to lessen the possibility of internal injury.
Grab something to keep you warm once outside (if time)
Cover your head with a pillow or other soft object. Brace yourself for impact so that you will move as little as possible.
Lastly! GET OUT! Often, people sit in the plane in shock. GET OUT!