The first piece of advice Google gives is to get involved with the community around your topic. If you were still not convinced that social media plays a very big role in search, consider this is coming straight from Google. Now the networks your community hangs out in may vary, but engaging with the community is simply a good way to get links and build credibility, which also will most likely lead to more links. Engaging is good for increasingly visibility outside of search anyway. Nothing new. Just reiterated by Google.
Another tip Google suggests is to create content that solves problems for your users - things like tutorials, videos, and tools, surveys, research results, etc. Users who find helpful content are likely to pass it on.
Google notes that humor and other link-bait tactics can work for the short term, but does not recommend counting such tactics. "It's important to clarify that any legitimate link building strategy is a long-term effort," says Google Search Quality Strategist Kaspar Szymanski. "There are those who advocate for short-lived, often spammy methods, but these are not advisable if you care for your site's reputation. Buying PageRank-passing links or randomly exchanging links are the worst ways of attempting to gather links and they're likely to have no positive impact on your site's performance over time. If your site's visibility in the Google index is important to you it's best to avoid them." (emphasis added)
"Directory entries are often mentioned as another way to promote young sites in the Google index," says Szymanski. "There are great, topical directories that add value to the Internet. But there are not many of them in proportion to those of lower quality. If you decide to submit a site to a directory, make sure it's on topic, moderated, and well structured. Mass submissions, which are sometimes offered as a quick work-around SEO method, are mostly useless and not likely to serve your purposes."
Szymanski also suggests looking to similar sites in other markets for inspiration - not to copy them, but to see the things that they have done to be successful and see if there is a way to apply that to your own site.
Finally, probably the most obvious tip offered here is to make it easy for people to share your content. Things like Facebook "likes" and Twitter retweets can go a long way in creating new links to your content. Granted these won't necessarily boost you "pagerank" but they will boost your visibility, which can lead to more quality links, and simply traffic, which is ultimately the goal anyway right?