Your link profile is potentially the most powerful aspect of your SEO efforts, especially in the eyes of Google. Quality counts over quantity, but it is important to get a good list of well-balanced links pointing to your site. Diversification really is the key. Try not to concentrate all of your efforts on gaining links from one source, and similarly try not to gain them using a single method. A number of tactics should be avoided wherever possible because they either offer you no benefit whatsoever or your page may be penalized.
This article looks at the acquisition of links purely from an SEO standpoint and, aside from the really bad linking methods, if a link will provide good-quality, direct traffic then it is definitely still a good link and well worth considering. You will have to use your judgment on this, to a certain extent.
Directory Links: Directories are viewed as being a very positive source of links by a number of search engines. Obviously, some directory listings carry much more weight than others and some directories are hardly worth the effort. Be careful to drip feed your site with directory links at first because it is possible that too many too quickly will see your site penalized until your link profile becomes more natural.
Start with the major Internet directories and consider getting links from free general topic directories as well as niche directories and also look at paying for inclusion in one or two of the seriously large directories like the Yahoo directory and business.com. As your link profile expands you can add more directories to gain extra weight.
Reciprocal Links: You may have read that reciprocal linking is dead. While it is true that Google and possibly other search engines now place much less weight on a profile that is crammed with nothing but reciprocal links they still have a place. Keep the number of reciprocal links you use down to a minimum and certainly don't base your entire link building efforts on this one tactic alone.
Again, balance is a big part of reciprocal linking but also of importance is relevance. Regardless of whether you offer a separate links or resources page, or you choose to include the links throughout your site you are still essentially endorsing the site. You will also gain much more credence from a link that is placed on a page containing information relevant to your own page.
Unique One-Way Inbound Links: These should pretty much be the staple diet of your link portfolio. An inbound link that is one way does not necessitate the inclusion of a link back to that page on your site. This can help to give your own pages the benefit instead of handing it out to your link partners. The more relevant and the more important that search engines deem the linking site to be the more weight they give that particular link.
Site Wide Links: Again, these should be used sparingly. Gaining a site wide link means that a link to your site or your pages is placed on a number of pages in a site. Search engines are known to give less weight to links that are procured on this basis but it does help to give your portfolio a more rounded appearance.
Press Release Links: Writing and submitting a digital press release can provide good links. Many press releases are used by other sites and industries related to your site and they may also be included on some major news websites. There are free press release distribution services available, but it is common to need t pay to make the link clickable and to use anchor text.
Article Links: Writing and submitting articles to article directories can provide a large number of links. Not only can you submit one article to numerous directories but each directory has the potential of generating a number of interested websites. These websites also publish your article (which includes an author bio section with your link). This can be a good way to get authoritative sites to link to you.
Community Links: Join forums and include your link in your signature. Post useful comments on other people's blogs and include your link as your username. You should, under no circumstances, spam blogs or forums and only include links on the sites that allow it.
Presell Advertising Pages: Some websites will allow you to include an entire page on their site. In most cases you will either need to pay to have the page written or you, or write the page yourself. Generally the website will also include other forms of advertising but as long as you choose sites carefully this can generate some excellent links.
FFA Sites: An FFA, or Free-For-All page, is one that allows anybody to post any link they like on the page. Typically they are not only useless to your cause, because the search engines ignore them, but they will not generate any natural traffic but may attract the spammers to your doors.
Link Farms: A link farm is a page that contains an excessively large number of links. Some say a page with 100 links directed out of that page is a link farm, but in all honesty it is unlikely that a page will yield much benefit for SEO or non-SEO with more than fifty or so links.
Off Topic: Off topic links are something of a bone of contention. They may offer very slight weight with some search engines because it is quite possible that natural links from certain websites would point to any number of pages on any topic. This appears in the bad link section because they offer very little positive benefit and your efforts would be best placed gaining on-topic links.
Unindexable: Purely from an SEO standpoint, links that cannot be indexed by search engines are completely useless. A search engine spider must be able to follow the link to find your page and provide you with any benefit for that link. Avoid any page that offers to display your link in a frame, or includes the noindex or nofollow robots.txt tags. However, bear in mind that a site that is currently not being indexed by search engines may be a new site. It could also grow up to be the next Google.com and take your link with it.
Your link profile should appear as natural as possible so vary the good links as much as possible and avoid the bad links. Collect links from as many sources using as many tactics as possible and use keyword variants in your anchor text. By following these guidelines you should be able to improve the appearance of your link profile and, therefore, improve your search engine rankings.