Anything that straightens out the Eustachian tube will work to some extent. Yawning, swallowing, stretching the neck (one side at a time, don't hang yourself!) and the valsalva manoeuvre all work. Some better than others in some people. It's better to start early as the greater the pressure differential, the harder to equalise it is. Similarly, if you can't clear your ears, it is better to ascend to a more comfortable altitude, clear your ears there and then descend again rather than putting up with the pain. Too much negative pressure in the middle ear can cause either a punctured eardrum (which relieves the pressure instantaneously but is rather painful) or, if left for a long time (or done repeatedly) a chronic overproduction of the mucus in the middle ear. It is basically the bodies attempt to equalise the pressure by adding volume (fluid, not air) to the cavity. This fluid can get thich and infected and can itself block the canal and prevent further equalisation of pressure. Chronic inflammation of the area will make the tube narrower and harder to clear.
All reasons to treat it early and prevent the problem in the first place (by not flying when you can't clear your ears). When on the ground, do a valsalva (pinch your nose and blow). If you don't feel/hear a pop in both ears then you may not be able to clear your ears. The problem may not become apparent until you try and descend, by which time it is too late!
I suppose another trick that would work is to maintain altitude but reduce cabin pressure. Make sure you don't get carried away or the masks might drop down and scare the pax!