If you have a web site, you may be getting more and more traffic. When you reach a certain threshold, you earn the attention of not only legitimate users, but other web site operators who want to work together with you to help you both gain more visitors. They'll probably email you out of the blue and ask to start link-sharing agreements. Link-sharing is an important part of a growing web site, but not all link-sharing offers are beneficial to you, or even legitimate.
Most link-sharing ideas are trying to game the system that search engines have created to rank web sites. Of course, the most popular search engine right now is Google, and its page-ranking algorithm that it uses is strictly a trade secret. It also keeps vigilant watch over its search results, and punishes web sites which have used misleading or dishonest means to gain their page rank by relegating them to a secondary index - the Internet search equivalent of Limbo. So see, this already has the makings of a great story. You've got trade secrets, people who try to game the system, crime, punishment, and Limbo. What more could you ask for
But before we get into a detailed description of link sharing or other ways to increase traffic, we should first describe the system that link sharing is meant to interact with. Google's PageRank algorithm is the stuff of legend - it makes or breaks new Internet businesses all the time. Google indexes all sites by keywords, what information they have in text on their site. But Google often gives hundreds of thousands of results. Which results are the most relevant is one of the most important secondary concerns that the Google search engine takes care of, and the real reason for its popularity. You might be looking for the #1 spot for Beatles lyrics on the Internet, but a search for "beatles lyrics" can turn up hundreds of thousands of web sites. How can you make sure that the first few, more relevant, results be about the words to songs that the British band the Beatles wrote, rather than the one page of some guy who named his Volkswagen Beetle "lyrics" and decided to write a page about it Google solves this problem by using Google PageRank.
With a secret method, Google assigns each web page in its search index a rank. These ranks are simply from 1 to 10, with 1 being the least relevant and informative page for a certain keyword or search string, and 10 being not only relevant, but extremely popular, helpful, and well-known sites on the Internet. All of the web sites on the Internet are arranged on this ranking in a sort of bell curve, with the large majority of sites being around 4 or 5. Popular destinations for specific uses, such as an actual Beatles lyrics site, can get a page rank of 7 or 8. Extremely well-known sites with millions of visitors per day and the highest standards of information on them can get 9. A very few sites, such as usa.gov and cnn.com, can have a PageRank of 10. Google also gives itself, google.com, a PageRank of 10.
Google uses a large mashup of information to determine a site's PageRank. One of those pieces of information is the number of links that point to a given site. Also, what kind of text is surrounding this link. If there are many sites which have text talking about a specific subject, like cell phones, and they all point to our web site, we would get a higher PageRank when cell phones were searched for on Google. Also, a second but still important aspect of PageRank is the number of links that point from a particular site to another one. If a site has a large number of both incoming and outgoing links, it can be considered a hub of information on one or more topics, which factors into the site's PageRank. There are a number of other secret factors that are said to go into a PageRank, and Google does not release the information in order to try to avoid people manipulating the system.
Gaming the System
While Google's purpose is to try to give the most accurate search results possible, web site creators vie for a coveted high PageRank for one or more keywords. Because, of course, more popularity in Google means more traffic, and more traffic means more advertising revenue. This may be the first time in history where one company is responsible for the success of so many others. Google holds the fortunes of millions within the palms of its digital hands.
So people try to manipulate the system anyways. Link exchange programs are one of the most popular ways to do this. Web site owners may try to actively drum up more links to their own web site in order to increase the popularity on Google. There are several ways to go about this, some of which are worthwhile, and some of which will backfire on you.
The best kind of link exchange happens without active effort on your part. Internet users simply find the content on your web site interesting, and link to it. Perhaps they run a blog, or edit a wikipedia entry, or make a forum post with your link in it. These all help you to gain reputation and popularity with Google, and benefit you.
Another kind of link exchange is done with a lot of work on your part. Instead of just waiting around for people to find and link your content, you yourself can peddle your site around the Internet, going around and posting links back to your own articles on other people's blog comment sections, forums, or wikipedia entries. This might be a little annoying to those people who run those sites, but also might help your own web site's reputation to grow faster.
A third kind of link exchange begins to involve other people. You can create agreements with web sites that share a similar topic or interest with your own, and agree to give some links to their site in exchange for them giving you links in return. This can also help your online street cred as part of a growing body of work relevant to one or more keywords.
You can also pay Search Engine Optimization (SEO) people to do all of the above. This is where things get risky, because you are artificially trying to inflate your PageRank with cash. You can pay some gentlemen in another country to spread links to your sites all over the Internet, and they will do so. However, it may be possible that it will look too artificial, and then Google with lower your PageRank without telling you. Or, it may relegate your pages to the Limbo of the secondary index, as mentioned before. How artificial and sketchy things look, and whether or not you get caught, depend on the quality of the links you create. If you have ever visited an unregulated or abandoned blog, you might see some of the poorest quality links show up in the comments. They just have a bunch of keywords crammed together into a huge paragraph, and the whole paragraph is linked somewhere. It is debatable whether this kind of brute-force tactic is even effective, and yet it happens with surprising regularity. A more elegant solution is for one web site owner to pay a firm to write relevant, content-specific articles which link back to his site. This is almost an undetectable way to increase page popularity, but will undoubtedly cost more money.
Of course, if you are concerned with authenticity or simply have a budget too small to hire anyone, you can always just let your web site grow naturally. And, if you have high enough quality content, it will do so without much prodding from yourself. Its all up to you.