Knowing your audience up front will answer many of your questions and save you from some costly mistakes. They are good for promoting a sale or a special deal on your product or service. Newspapers carry a lot of ads, however, so there is a risk that yours may get lost in the clutter. Magazines offer a slightly better opportunity to catch a reader's attention than newspapers, but the ads typically cost more. Magazines are good for promoting your company's image and building its credibility.
Repetition is especially important in radio advertising.
In your case, advertising on the right station at the right time of day might make a big difference. Television advertising is extremely high-impact, but it is expensive. Cable channels are more affordable, but are seen by far fewer people. Yellow Pages advertising is not cheap, but it delivers people who are ready to buy, now. Outdoor advertising offers high visibility, and the cost per viewer is relatively low.