Given that more than 90% of both business-to-business and local consumer purchases now begin with online search, search engine optimization (SEO) has become essential for business success. Little wonder then that two-thirds of small to midsized-business owners plan to increase SEO efforts this year.

While specific best practices for SEO have evolved over time, the two core attributes for high rankings have remained constant: relevance and authority. Relevance is determined by the subject matter of a website and on-page optimization techniques (e.g., using keywords in headlines, meta titles and image names), while authority is primarily based on the quantity and quality of incoming links to a website.

So, once you’ve developed useful and compelling content, incorporating the words and phrases your customers are likely to use when searching, how can you attract links to your site? Here are four helpful sources to go after, and three others to stay away from.

Four Worthwhile Link Sources

1. Local directories and high-quality industry directories. Virtually all businesses can benefit from providing their company and contact details to the local versions of Google, Bing and Yahoo!, as well as online yellow pages and other similar directories. GetListed.org, a site that evaluates your business presence and directly connects to more than a dozen such directories, is a great place to start.

   Industry-specific directories, often published by trade associations and publishers, are another important link source. You can often find the most authoritative (in the eyes of the search engines) directories specific to your type of business simply by searching for them. For example, if you own a restaurant in Minneapolis, a Google search for “lists of restaurants in Minneapolis” returns more than two dozen lists just in the first three pages of results—some general and some specific to certain neighborhoods, categories and price ranges.

2. Business partners. While linking to irrelevant sites purely for SEO purposes is not advised (see “Reciprocal link schemes” below), trading links with business partners and complementary firms is helpful both to visitors and your rankings.For example, a manufacturer may trade links with retailers that sell its products, service providers that install or fix those products, and even suppliers of key components. As long as the links are topically relevant and connect high-quality sites, those links have SEO value.

3. News and media coverage. Links from industry news sources are among the most valuable for building authority. You don’t have to get links from the New York Times or the Wall Street Journal (though if you can, obviously, that would be very cool) in order to improve your search rankings; links from relevant trade journals and local media can also have significant value.One method for obtaining links is to create search-optimized news releases and distribute them through an online service like PRWeb. Another is to work with journalists directly, or hire an agency to help you. Announce a new product, get your executives or other subject matter experts quoted, help out a local charity, speak at an industry event—all are great sources of potential media coverage and links.

4. Social media. Create business accounts and actively participate on Twitter, LinkedIn, Facebook and Google+. If you’ve got a highly visual product, use Flickr and Pinterest; if you can make video part of the mix, set up a company channel on YouTube and Vimeo.

As the search engines make social signals an increasingly important element in rankings, the links that you create—and that your customers, followers and industry influencers share on your behalf—take on greater importance for SEO.

Three Links Sources to Avoid

1. Reciprocal link schemes. Unlike legitimate link-trading (see above), link schemes are manipulative practices designed to “trick” search engines into giving your site a higher ranking. Such links have little or no value to your site visitors.These links are generally to sites that are completely unrelated to your business and often to somewhat sketchy destinations (e.g., online casinos, “miracle” weight loss products, get-rich-quick schemes or questionable web pharmacies).Such schemes are still around because, as with other manipulative practices, they actually worked at one time. But with recent changes made by the search engines, particularly Google’s Panda and Penguin updates, such tactics are now far more likely to hurt rather than help—and may even get your site banned from search results.

2. Purchased links. If you come across online advertisements touting “1,000 Backlinks for $14.00” or some similar offering, run—don’t walk—away. Buying links is not only no longer an effective strategy, it is highly likely to get your site penalized. These links are very often low-quality, containing hundreds or thousands of unrelated and often low-quality outbound links, making them easy for search engines to spot.

3. Low-quality general directories and “bad neighborhoods.” As noted above, directory links can be helpful for SEO. But not all directories are created equal. Search engines will confer authority on your site for links from high-quality directories, but frown on links from low-quality sources.Since “quality” is a subjective term, before pursuing a link from any site, ask yourself: how likely is it that your actual customers or sales prospects would ever visit this site and find you there? What other types of businesses are listed? Would you be proud to be listed there or a bit ambivalent about it? Does the site offer value to visitors, or is it essentially just a large collection of unrelated links?

In short, search engines want to direct searchers to the most relevant and useful results for any search query. Seeking out legitimate link sources to help guide search engines to your site is perfectly acceptable, and helpful to your search rankings. But avoid any sort of manipulative linking practices designed to deceive. The old Chiffon margarine commercial said “It’s not nice to fool Mother Nature.” It isn’t nice to try to fool Google, Yahoo!, Ask, AOL or Bing either.