Ask permission if you wish or just place them if you don't want to ask. If not asking there is a better chance it will be thrown away. For a better response, place your ad in a targeted place. If you market a weight loss product you may want to leave your ad in the candy section or in the ice cream freezer at your favorite supermarket. This makes sense.
People often think of dieting when they are gorging on sweet stuff.
Place your ads in elevators, in the dollar bill slot in coke machines, attached to the handle of the gas pump. The possibilities are endless. Just use your imagination. Every month when you get a bill they have placed advertising inserts. When you send in your check to pay your bill, simply send along your ad.