The only really distinguishing feature of this type of cover letter is that the opening paragraph generally includes a statement such as “I’m responding to your advertisement I saw in the…”
The rest of the cover letter generally follows the principles of other successful cover letters. However, if you find yourself going through the classifieds in your local newspaper and simply sending off cover letters to whomever has an ad posted, do make sure that you do some research on the company before you send out your cover letter.
Sending one cover letter out for multiple advertisements is a good way to ensure that you won’t be getting too many interviews in the coming days or weeks.