I'm in the midst of doing exactly that right now -- marketing myself (not here, of course). In fact, I'm in the process of trying to form a virtual firm of a number of patent practitioners with home offices. Some of the other attorneys have contacts in big, publicly traded companies and I'm getting introductions that way.
Before you "cold call," check with your state's ethics rules. Many prohibit that activity. Mind does (Calif.). You have to have some prior relationship with the callee or have no reason to believe they specifically need you services.
The right answer (in my opinion) is networking. But that's too broad of an answer; it's like telling someone to catch fish by putting a line & hook in water -- not nearly specific enough.
I've been to all kinds of networking events recently. I'm noticing different types of networking events. 2 types are particularly useful. One is the type in which business owners/officers go for general IP information. I made 3 solid contacts at the last one I went to and I'm going to another next week. Another is one in which other IP attorneys (not patent, but licensing, litigators, etc.) lure potential clients with an afterwork mixer -- open to the public. Many of those attorneys are easy to approach because they're schmoozing too. I find a number of them aren't happy with their current patent referrals and would like to send clients to some place better.
What geographic region are you in? Maybe I can point you somewhere.
And, if you see me at one of these events, be sure to say nice things about me! ;-)
Regards.
P.S. Don't bother with Venture Capital events. VCs aren't particularly impressed with IP and everyone else seems to be in BizDev and doesn't fully understand their technology anyway -- and are looking to get money, not spend it. The VC community is slowly catching on about IP, but slowly. And, they seem to have a limited attention span (or, more likely, a limited attention budget) -- explaining IP to them isn't likely to produce results, especially if there's a line of people behind you ready to ask for money.
FWIW, many VCs are a bit hostile to IP. I don't think it's for reasons based on the policy behind IP, but rather that IP complicates their analysis. Capitalists like to assume no barriers to entry, but that's exactly what IP is. To many, I explain that my job is to erect barriers to entry.
I hope that helps.