Let the potential customers know exactly what it is that you want them to do. If the, “Sale Ends Soon!” be more specific and tell them what “soon” means; “Sale Ends Saturday!” Be concrete. Using abstractions makes way for misunderstandings. Being specific and using concrete descriptions is the best way to anticipate that the message you are trying to communicate is going to be understood by just about every consumer.
I got this from US Newspapers. They are a newspaper agency, that I have placed ads with. If you need some help they are a good starting point. http://www.usnewspapers.com