Class of mail, address service requested

[David S.]

I'm sending out my first set of postcards and letters this week, and  need some advice on the mailings. Do you need to do anything extra to get the post office to return mailers to you besides making sure your address is on them? I've read that depending on the class of mail, postcards get trashed instead of being returned to the sender or forwarded. 

Do I have to add 'address service requested' or something similar to get them back, or the letters? I've browsed the USPS website, but it hasn't been helpful or clear.