The first step to link building is competitive analysis, unless you're the first mover in your market. If your competition's already found sources for links, chances are you can use the same source.
People often ask, "what do I need to do to build links?" Inevitably, they get the same generic answer: build content and make your site worth linking to. What if you're all about e-commerce or something where content isn't really relevant?
The answer then is in the second part of that generic answer, "make your site worth linking to." That means two things:
1) You need to solve their problem. A constitutional law site is never going to link to a casino site, unless there's a convention at the casino. But that won't happen because constitutional law profs are boring old farts who don't gamble. You can get a link if you're some fancy convention center where the old farts will be meeting though. The point is to define problems your company solves and go inform people, so they can share the solution by linking to you.
2) Establish a relationship with the person in question. If they're an SEO or someone who understands the value of links, and you've produced something good, a simple email will usually be opened and responded to. In the non-marketing world, emailing someone about a broken link on their site, bad navigation, typos etc. tends to make you seem friendly and make people more receptive to your link suggestion.
The added benefit of this approach is that you can go to them for more links in the future and ask them for referrals to their friends. Yes the net is impersonal, but networking still exists.
Now the thing is that when you don't have a content site, it's hard to figure out whose problem(s) you can solve. Luckily, you don't need to be so clever and original. You can just copy your competitors. Get the same links and add them to yours, and you'll outrank them. Which is where backlink analysis comes in handy, and particularly this tool from that well-known (and pricey) link-building ninja, Jim Boynkin.
The tool lets you discern which common links your competitors have (and thus which ones you can also probably get). Additionally, it tells you which ones the search engines are looking at, so that if you're not sure where to start, you can go for those at least some of your competitors have (as opposed to one you ran into while doing competitive analysis by Googling their brand, for example).
Next time: Social networking and link building, my ultimate link-bait post.