What a great question. Developing the advertising component of the marketing strategy is critical -- and your commitment to doing it right from the get go reflects a solid understanding of the dynamics of today's business environment.
There are several ways to identify the best strategies of your business. I am sure that you will get lots of answers on here about the power and importance of blogs, PPC, SEM, SEO and lots of other web-based strategies. (Including to your own question) I wont add to those -- as I am sure what you here from them we will far more valuable then what you would hear from me.
What I would like to address are three points: Where to start, Embracing Trial and Error, and Ensuring you have the Systems.
Where to Start
The simple answer is go where your customers are -- and then focus on where they are when they are making a decision about who to use for a break & fix computer business. You know your market and you know your target customer. You know their demographic, and by providing quality service you have learned when and how they make a decision. You want to show up in front of them -- when they are about to make the decision.
You need to be able to have a level of specificity for your target customer that is so "tight" that when you talk to a radio/cable/multi-media provider you will be able to discern exactly what (if any) program they are listening to. You know their business size. You know who owns them. You know why they choose to use your type of service.
Look at other companies that are serving the same customer and see where they are advertising. Perhaps it is your competitors-- and you see their ads in a business journal, or in a specific newspaper. Perhaps you hear their ads on a specific radio station. Perhaps you see their billboard on a specific interstate. Learn from your competition. And there are companies serving the same market that are not direct competitors. Perhaps it is an office supply company? Or a shipping provider? Look around the offices of your clients and see who else they use -- and then scan the advertising market to see where these companies are advertising. When you find the overlap you will have tangible information of where it might make more sense to advertise.
But the most important -- is ask your existing customers. Have a customer survey that you incentive to get responses -- find out what they read, what they listen to, what events they go to that you could sponsor, who they ask when they are looking for a referral. You don't even need a survey-- just talk to them and ask. Listen. Ask. Listen. Ask. Listen.
Embrace Trial and Error
I appreciate that with the tight dollars of a start-up you would like to avoid trial and error as much as possible. Trial and error does not mean shooting inn the dark. Use all of the strategies above to make an educated guess. But that is a trail. And now you need to make sure you are constantly testing it and re-testing it. As markets change, and customer behavior changes what advertising works for you will also change. This will be ongoing for the life of your business.
Ensure Your Systems
Make sure you have a good CRM set up. You need a CRM that allows you to manage your advertising and outbound marketing campaign in a way that connect leads, prospects and customers with the source. You need this to support your ongoing trial and error -- as well as calculations on the ROI of your marketing and advertising expenses. It will also allow you to calculate the total life-time value of a customer so that you can better judge what your marketing/advertising budget should be.
The most important thing you can do in your business is to build a happy cusotmer base that refers others to your business. Don't throw out old school techniques just because they are from a previous generation. A physical leave behind that keeps your name in front of your customers might be a great advertising play. Perhaps something they would pick up when they are stressed as their computer is rebooting? Something that reminds them it might just be easier to call you?
I don't know -- but you do -- when are your prospective customers thinking of your services and need to be reminded to call you. Own that moment.