If you have flat feet you need to address them. Flat feet/collapsed arches/etc. tend to manifest themselves with eversion of the foot..
http://www.biggerfasterstronger.com/uploads2/08_JanFeb_FlatFeet.pdf
And to follow up on that, some advice for anyone who engages in the journey of finding insoles to help, what worked well for me were Superfeet Insoles. The pair I had before that were VERY flexible, and under my weight they barely stood up at all. The pair before those, my first pair which I was given personally by a long-time physical therapist, stood up well; but, 4 months after receiving them I accelerated quickly from a still position to a sprint, and broke the internal support structure of one of them.
Also... when you listen to your body and feel ready for it, start doing exercises for your support muscles - calve raises, shin raises, foot eversions, inversions

(standing of course), etc. If you have flexible arches (I can't speak for people with stiff flat arches), you can adjust your stride, monitor your posture, and make use of the support muscles in your feet and ankles to give* yourself arches and control eversion.
*"give" is a poor choice of words, but I hope you get what I mean.