Hello everybody!

Recently I have noticed that my braking has gotten bad. It takes very long to come to a full stop or even slow down a little. I have cleaned my rims which helped a little but not too much. I wanted to know if sanding the braking surface is a good way to improve braking. It sound like it will help, but will I ruin my rim? Is there a special way I should sand them?(wet or dry). Thanks!

By the way I have kool stop dual compound pads on both front and rear.