Purely anecdotal, gently massaging the angle angle under the jaw seems to work for me, Valsalva tends to make things worse.
I guess the theory behind increasing the fluids, is to reduce the tenacity of the gunge circulating around the eustachian tube. (Again, this tends to work for me, not sure about the science behind it.)
Avoiding spicy foods the night before, also seems to make a difference.
I spent my last flight, watching the effect of altitude on the plastic wrappers around bread rolls, and sealled plastic water bottles. Fascinating stuff, no wonder some of you guys are always feeling ill.
Robert Boyle has a lot to answer to.