In the ecuation of Adsense optimization income you need to chose the right markets, provide tons of quality content and achieve backlinks to your websites.

Link popularity, in a very simple definition, refers to the number of pages that link to a given web site. Incoming links are the most important factor in generating traffic for your site: they drive visitors directly to it and they are the most important element considered by search engines to determine the order of their search results. However, link popularity is not about receiving as many links as possible.

Link building is the process of researching, requesting and encouraging links to improve a web site’s link popularity. But, is this a SEO task? In order to answer this question we must define two types of incoming links that are often distinguished (specially by search engines) based on their nature:

• Natural links: Those that are due to the intrinsic nature of the Internet: people publish web pages and include links to resources that they consider useful for their visitors. Natural links are not requested, but given voluntarily and spontaneously. They use to have different anchor texts, are rarely reciprocal and increase gradually over the time. There is no direct way to get natural links for your site, unless offering a great content and wait for others to link to your pages.
• Artificial links: Those that are requested in any way: link exchanges, paid links… Search engines tend to ignore (or in abusive cases, even penalize) these kind of links. Artificial links use to have identical or similar anchor texts, are often reciprocal and increase suddenly when the link campaign starts.

  There is an even more obvious type of artificial links: link spamming. Take into account that not all artificial links are spam, but of course all spam links are artificial. Link spam techniques include:

• Link exchange programs and networks: Using automated or semi-automated methods of exchanging links between several sites.
• Link farms: Submitting a web site to pages with no other content than hundreds or thousands of links to other unrelated pages.
• Guestbook and forum spam: Posting useless comments in guestbooks, forums and other similar sites with the only purpose of including one or several links.
• Blog spam: Similar to the previous point. Making use of comments and trackbacks to post links in a blog.
• Hidden links: Including links on a web site that are indexable for search engines but invisible for humans. These links are usually used to create link networks in order to increase the link popularity of the participant sites.
• Referrer log spam: Some sites have a referrer log that shows which pages link to them. This technique consists of making automated accesses to that site from a link placed on a spammer’s page, so the log will include a link to the spammer’s site.

Search engines are the main reason why link spam exists, specially since Google started considering link popularity as one of the most important ranking factors and created a measure for it (PageRank). However, those same search engines are now the main link spam fighters. Link spam techniques are severely penalized, and you should avoid them for any succesful and long-term search engine marketing campaign.
According to the above, artificial links are useless or even harmful for your web site, and natural links can’t be obtained in an artificial way, so, how do SEOs work on the link building strategy?:

• The zone between natural and artificial linking: There is a thin, vaguely defined, zone between both types of linking. It’s something artificial in the way that it’s requested, and it’s natural in the way that it corresponds to the nature of Internet: making submissions to very relevant and high-quality directories, sending emails to webmasters that could be legitimately interested in your web site (and could potentially link to it), encouraging links in any way… These techniques won’t harm but, on the contrary, could ultimately improve your web site’s link popularity.
• Masked artificial linking: A risky strategy consisting on getting artificial links and trying to make them look natural to search engines: Exchanging non-reciprocal links, paying for them in a few very popular sites, varying their anchor texts, getting them gradually over months and not in a few days… Currently people use to mix the terms SEO and link building. So, to make it clear, these are different but complementary concepts:

SEO is a wider concept than link building as it includes the optimization of on-the-page factors. Link building is a wider concept than SEO as it includes other marketing strategies aimed to improve the web site’s quality and exposure and hence encourage the natural links to it.