If your Web site isn’t getting the attention it deserves on the Internet, it may be running low on Google juice.

Google juice, for the uninitiated, refers to how high a Web site ranks in Google’s search results — the higher the ranking, the more juice. Google juice is all about links. As many people know, the Internet search leader ranks Web sites based largely on the quantity and quality of other sites linking to it.

It’s no wonder that a whole new industry has arisen around mining the Web for links and other page-tweaks that can help sites boost their Google rank and reel in more visitors. This industry deals with “search-engine optimization” (SEO), and search engine marketing companies specialise in this.

Many of these search marketing companies focus on natural search marketing and helping people get, and keep, their websites in the top ten of Google searches for their particular search term. This is done by having lots of links from other websites to the site, as well as the website itself containing good quality written content. It is important too that this content includes terms which are relevant to the purpose of the website.

Google, however, takes a dim view of attempts to artificially manipulate search results, and can indentify unnatural content (content which is stuffed with links and search terms). This is why it is best for businesses trying to get to the top to consult a search marketing agency that knows exactly how Google works and the criteria it uses to rank websites.

Google is constantly updating itself, and in recent times it has gotten much harder to influence Google results for popular searches, which is why many consultants advise businesses to encode their sites with specialty phrases and keywords related to the business that people might type in the Google box.

Jim Westergren, a Swedish search consultant, said he thinks it’s “very hard” to game Google today, particularly since it keeps improving its link analysis: “Recently Google has been getting more smart about this and can even detect and devalue paid links,” he wrote.

Rand Fishkin, chief executive of a Seattle-based search consultancy called SEOMoz, said he focuses on getting editorial links for his clients, partly by creating feature articles that Web publishers will link to: “We call it link-baiting. The idea is to attract a lot of natural links.”

Bill Leake, chief executive of Apogee-Search.com, a consultancy firm in Austin, said links are still the key to impressing Google. He advises businesses to take a two-step approach to boosting their Google rank. First, they should test search terms related to their business by purchasing Google ads for those words, which allows precise tracking of ad click-throughs and purchases. After learning which search words yield the best results on ads, businesses can hire a consultant to embed those terms into their sites and buy links relating to them.

“The link brokers are going great guns,” Leake said.

One such firm is TextLinkBrokers.com, which started in Phoenix three years ago by brokering paid links between sites with high Google ranks to those with low Google ranks. But Google’s changing formulas have made it harder to boost a site’s ranking just through paid links, said Jarrod Hunt, chief executive of the 60-person firm.

“Editorial links are more valuable now than the paid ones,” he added.

Hunt said his firm still brokers text links for sale from thousands of independent Web sites, but it also develops original editorial content to help get links Google might consider to be of higher quality. Often the articles are given away or sold to sites in a program he calls “hosted marketing pages,” basically online advertorials with embedded links.

There are shady ways to get Google juice, too, but be careful — it could get your site booted completely out of the Google index. If you break the search-engine rules, the juice can turn to poison and lead to the Google death penalty.