Selected answers from the Dumb SEO Questions G+ community.
Ryan Jones: Build something that people think is so cool or so good that they want to share it with their friends.
Jim Munro: Reach out to your clients and suppliers.
Michael Martinez: One thing I rarely see any more is people putting a request for links at the bottom of their content. There is no search engine guideline against doing that. A simple request in the form of "If you like this article please consider it sharing it with your friends when it fits the discussion. A link from your blog will also be appreciated." Something like that.
George G.: build a free tool. think of smth that can automate a task in the niche. then outreach, make pr, msg niche organizations and schools that might use it for free. this works extremely well.