The first, perhaps most important step is to stay away from orthotics and shoes with “plenty of arch support.” Rather than help you solve your problem, shoes with arch supports prop you up and lead to weak, atrophied foot musculature. Your feet aren’t grasping, pulling, pushing, and flexing inside a pair of athletic trainers; they’re growing soft and growing weak. Fixing, or at least mitigating, your flat feet is going to require some serious foot strength.
Next, spend as much time as humanly possible with your bare feet. If you’re at home, remove your shoes as soon as you enter. If you’re heading out to take the dog on a walk, try circling the block in your bare feet. Mail’s come? Shoeless. Early morning paper? Barefoot. Living room workout? Do it without shoes on. You’ve got to learn to use your feet again, and the best way to do so is to simply live, eat, breath, and sleep barefoot.