I think that the first question you should ask is not "how to advertise", but "to whom should I target my advertising". In order for marketing to work, it have to be really targeted and specific. You can't be everything to everybody. You have to propose some specific benefits that resonate with some problems that potential customer have.
Can you identify some people or companies that might be interested in what you propose? Who would benefit the most from your services or solutions? What are the solutions that you delivered again and again and who needed them? To whom your best solutions can provide the most value? the most ROI? Is there a customer segment where you can make a compelling case that one of you solution help the make more money?
Before advertising, you might want to talk to has much potential customer as possible in order to understand:
1. there needs and problems
2. their buying process (this is really important in B2B to understand how they buy: who will choose, who will use, who will pay, etc..)