To get the most bang for your advertising buck, do niche marketing.
Find where your prospective clients congregate, and advertise there. It can be a magazine for your industry, a store that carries related products or any of many other places.
I knew a person who wrote a book on bird watching. He sold his book through various outlets, including: sporting goods stores, stores that sold bird seed and houses, newsletters for birding clubs and other related markets.
Knowing where your clients are is the key to successful advertising.
Let me know how well this tip worked for you.
There are more business tips on my blog at www.TheCreativesCorner.com