Don’t try to jump before collapsing
Jumping before collapsing might not be useful as the reduction in impact won’t be that significant, it would be hard to jump in the right time and you might hit your head.
If you have bags stand on them
According to lonely planet Standing on the bags you have might help reduce the impact of the crash. Stack the bags you have and stand above them if possible.
Spread your weight over hand rails
According to lonely planet hand rails can help reduce the force of the impact. If the elevator has hand rails then spread your weight on them to reduce the relative impact.
If the elevator is crowded slightly bend your knees
By slightly bending your knees you can reduce the impact a little bit. This can be useful if the elevator is crowded. This position will put most of the load on the knees and legs but it might protect the rest of the body.
Lie on your back
According to MIT the chances of survival can be improved if the whole weight of the body was distributed on the floor. By lying down on the floor in the center of the elevator and spreading your body the impact can be reduced.
Cover your head
When a elevator falls part of the ceiling might fall as well. Covering the head can help in protecting the head and the brain. (See Why Am I Afraid of Heights? Are you Acrophobic?)
Stay away of the doors
Research shows that most of the fatalities that happens because of elevators happen as a result of people being stuck in the wrong places. Staying away from the door can protect you from getting stuck between floors in case the door busted open.
Don’t stiffen your muscles
If you stiffened your muscles then the impact force might break the bones or damage the joints easily. Instead make sure that you are read to let your limbs bend or swing as a result of the impact. This can reduce the force a great deal.
Hold onto the ceiling
Some people suggest that grabbing something in the Ceiling of the elevator, if possible, can help reduce the impact. As the elevator his the floor the your grip will go loose and this will reduce the impact by a great deal. (See Why am I afraid of flying?)
Don’t sit on the floor
Do not attempt to sit on the floor if the elevator started falling. Sitting on the floor will put a massive part of the impact on your hip bones and spine.