Even though the commercial market is divided into a number of distinct segments, it is significantly smaller than the consumer market, and therefore is much easier to research. Commercial photographers typically focus on one or two primary markets such as advertising or editorial as well as a number of secondary markets such as design firms or PR firms.
This makes it much easier to identify specific companies within those markets – because those companies must market themselves to their clients, it makes researching them relatively easy. Researching clients will be covered in a specific tutorial, but at this point I can tell you that it is critical for you continually research the market. You should have scheduled time put aside to scout and research prospective clients, on top of continuing to research your existing clientele.