There's one problem that will derail your campaign and keep you from turning a positive ROI and it's this. If you run an ad in a magazine for example, the rep will tell you “Our distribution is 50,000” or whatever their number is. So you think wow if I can get 1% of that, I'm going to have 500 customers – this is awesome!
The problem is that out of that 50,000, there may only be 5,000 that are actually in your service area or willing to come to you. Out of that 5,000, there may only be 1,000 that are viable customers. Now that 1% isn't looking so good.
Think about what I just said above. Out of the 50,000 people, if only 1,000 are actual potential customers, that means you spent 98% of your budget, talking to people that aren't going to do business with you.
If you want to drive business, you need to target the right people. The better you target (and do all the other things above right), the more likely you'll be to have success with your ads.