What is link building?
For search engines that crawl the web, links are the streets between pages. Using sophisticated link analysis, the engines can discover how pages are related to each other and in what ways.
All Links are Not Created Equal: 10 Illustrations on Search Engines' Valuation of Links
Google's founders created an algorithmic method to determine importance and popularity based on several key principles(http://infolab.stanford.edu/~backrub/google.html):
Links on the web can be interpreted as votes that are cast by the source for the target
All votes are, initially, considered equal
Over the course of executing the algorithm on a link graph, pages which receive more votes become more important
More important pages cast more important votes
The votes a page can cast are a function of that page's importance, divided by the number of votes/links it casts
Used by Search Engines
Link Building Strategies
Resources/Links pages, Time: 2-4 weeks, Dependencies: Marketing, design, development, Link Value: Moderate-High.
Profile links (www.crunchbase.com), Time: 1-2 weeks, Dependencies: None, Link Value: Moderate.
Ask people you know for a link, Time: 1-2 weeks, ongoing, Dependencies: None, Link Value: High.
Get people to see your content, Time: 12+ weeks, ongoing, Dependencies: Social, Link Value: High.
Build relationships Time: 12+ weeks, ongoing Dependencies: Social, customer service Link Value: High.