There are no "social tricks" involved -- well, not in the sense that you're thinking. You don't need a magic mind control beam to sell things to businesses. Here, I'm a geek like you're a geek. Can you (or J. Random Hypothetical Dev) outline how you would convince me, a fellow geek, that you could successfully program iOS applications? Showing me something you have made would suffice. Talking about the process of building iOS applications in a way which made it sound like you knew what you were talking about would also suffice.
Now pivot from the technical question to the business question. Given that I (or K. Random Small Business Owner) has a business doing $FOO, how does that business make more money or spend less money as a result of having an iOS application built for it?
I know exactly how you'd sell me an iPhone app. You'd ask if any of my SaaS accounts had ever canceled because of lack of an iPhone app. I'd tell you that that happened X0 times. You'd say "How much was their aggregate spend per month?" I'd say "A few thousand bucks." You'd say "So, to a first approximation, an iPhone app being available is going to be worth a few thousand bucks per month to your company within a few months." (n.b. This is just an example rather than a request to get proposals, guys.)
How would you convince e.g. a financial adviser that he urgently wants to have an iOS app written? That might start with "How much do you make on your average customer account every year?" "A few thousand dollars." "How often do you get to talk to them?" "Mostly commonly, once or twice a year." "Do they ever cancel saying 'I don't understand what I'm paying you for." "That's my #1 cause of losing clients." "Wouldn't it be better if you were on their home screen every day?" "YES."
How would you convince a restaurant that they want want a delivery app? Fill in the blank.
How would you convince a plumbing company that they want something their plumbers can use to check-in and check-out of work sites? Fill in the blank.
As to where you find businesses: I suppose you could sell things door to door, but most people don't. One way which works for a lot of people is to throw an event with the local e.g. Chamber of Commerce about some technology topic (maybe an overview of how mobile is changing the Internet, a subject on which you're vastly more educated than the average owner of a firm with $2 million a year in revenue in your local community) and having business cards and a willingness to continue the conversation when people try to talk to you after the event.