Arch supports. A semi-rigid arch support is good place to start. You don't want a super flexible, soft gel kind. It should have plastic on the undersurface and cushion on top. It may be 3/4 length or a full insole. Spenco and superfeet are some of the more common brands and can be found in sporting good stores and some pharmacies. No prescription needed. If this doesn't work, a custom orthotic should.
Orthotics. Orthotics or arch supports can help your feet and it's arches. Many places now have something you can stand on, and based on a rough shape of your foot and arch it will direct you to an appropriate arch support.