I have flat feet what can i do to avoid knee pain?

Much depends on : What sort of symptoms you have. If there's pain developing, then most of the time the situation can be helped by the used of custom orthotics. Its all about the stability of the feet more than the literal height of the arch. As the foot flattens (pronates) there's a torque of internal rotation placed on the knees which can lead to problems down the line.

Orthotics: A good pair of orthotics. You can try over the countr ones if they don't work visit the podiatrist who can make custome made ones.

Orthotics: Custom orthotics work well to relieve some types of knee pain.

Orthotics: First and foremost, you should be wearing a shoe that has proper support. I often see patients with worsening issues during the summertime because they are wearing flip-flops which offer no support! so, no flip-flops. Also, orthotics can help tremendously, so using otc orthotics until you can see your dr or a podiatrist who can make a custom pair , is recommended.

Wear: arch supports and strengthen your quadriceps muscles.