I need to give a multi-faceted considerations as there's a lot more than just placing banners where they can be seen. For instance, do your potential clients even need or want what you are offering? Or do you need to educate them on why they need what you're introducing to the market?
Marketing is often thought of as part of the sales process, and to a degree it is, but in reality, marketing is the research that should be preliminary to the sales process, and hanging your banners may either be part of the marketing process, or part of the sales process, or both at a certain point.
What exactly do you want your clients to learn or know about your new service? Can it be explained via a four foot by eight foot or five foot by ten foot banner? Have you tested your message, or will the banners be your testing method.
Here's a suggestion.
Find a location that you can place a banner that passersby will see easily, if available. If not available, you may want to think of a different advertising venue, but many businesses have one or two locations where this would be possible, if they're not in a high rise office building in downtown Manhattan or the like.
Test Your Message
Assuming your business has a location or two like this, now test your message. Let's say you are introducing a new app for cell phones that you hope will rock the civilized world. This app will control all the computer functions in your home, from lights to heat to alarm systems. But it will take some education to get people to know why they NEED this app, and you're not giving it away for free like the bank does with an account app.
While there's many ways to go about this, and this is probably something you'd want to roll out nationally, you can do it cheaply on a local basis using banners because you have an easily viewable banner location. So you put out a banner for a week or two that states succinctly what your new app does (this needs to be readable in about three seconds as the vehicle drivers that are passing by have about that much time to read it.
A store employee in your store is instructed to poll persons entering if they are coming in because of the banner, and if so, directs them to the right person to explain the app and why they need it. By calculating the people who are generally entering your store because they shop there or were referred there by an associate, and those who are coming in specifically because of your banner, you can find out what percentage are coming in due to the banner's message.
After a couple of weeks, you can put a new banner out with a different message, and use the method in the previous paragraph again to ascertain what percentage of the customers walking through your front door are doing so because of the banner. If the percentage is greater with your second banner, you can discard the first banner's message, and after a couple weeks, try a new message. Testing this way will help you learn what makes your client tick, so to speak.
This method can also be used online or in print ads as well. It could even be used with billboards that have an associated code that is referred to when a person calls or logs onto your website to learn more about your product or service. This takes the guesswork out of your advertising, so that the location of your banner becomes less important in some regards to the message, although people still need to see it to read it.