I do the same as alexandra
![Smile :)](./images/smilies/icon_smile.gif)
Fold the SASE and put it inside the envelope, along with a letter and a photo to sign (if you are sending one)
![Smile :)](./images/smilies/icon_smile.gif)
However, you may have a problem if you are sending cardboard-backed envelopes, as they don't fold very easilly so you may wat to send a smaller SASE so that you can fit it in without folding it
![Smile :)](./images/smilies/icon_smile.gif)