When speaking to various area ad reps I'm amazed when they speak of small business owners who don't follow their advice. Now I can understand to be cautious when dealing with someone who's trying to sell you something. But once you've made the decision to advertise, it's smart to follow the path of those who are already advertising successfully.
An honest ad rep can help you there. Once you find one and you discover that they're interested not just in their wallet, then find out about their clients who seem to have good luck in advertising. Those successful advertisers typically follow a general format in getting response. You need to know what they're doing. A good rep will take the time to share that with you. After all, if you're successful, then you're probably going to spend more money for ads in the future.
Print advertising can be costly. This is an area where you need to be "on". Find an honest rep, then do some investigating.