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Some link building campaigns are more difficult than others. If your blog contains unique content that is useful to people, find your niche market. Hopefully the someone you email agrees that the content is useful and will link to it, also benefiting their users. If it has to do with products, again find your market. This can be more difficult, hopefully your products have features that similar products don't. Focus on those features when finding your target market. I would focus on emailing blogs/bloggers & websites personally instead of guest posting. If you get a response there's a far higher chance you'll get a quality link. If your blog has great content, you'll only need to do this a few times before more and more people find you. If you try many times with no success, work on your content. If searches about your content is highly competitive, focus on sub or even sub-sub topics about your content. Content is king!