What to do
If the masks don't drop it's going to be because there is no need for supplemental oxygen. The only thing remaining is dealing with the sudden pressure changes on the body.
I'm SLF but from my scuba diving training you want to keep breathing to keep the pressure in your lungs equal to that on your body - holding your breath can damage your lungs when scuba diving and whilst aircraft have less pressure range I assume the same things will apply. Just try clearing the ears normally remembering that you will have an initial decrease and then an increase in pressure.