By relying so much on factors such as keyword density which were exclusively within a webmaster's control, early search engines suffered from abuse and ranking manipulation. To provide better results to their users, search engines had to adapt to ensure their results pages showed the most relevant search results, rather than unrelated pages stuffed with numerous keywords by unscrupulous webmasters. This meant moving away from heavy reliance on term density to a more holistic process for scoring semantic signals. Since the success and popularity of a search engine is determined by its ability to produce the most relevant results to any given search, poor quality or irrelevant search results could lead users to find other search sources. Search engines responded by developing more complex ranking algorithms, taking into account additional factors that were more difficult for webmasters to manipulate. In 2005, an annual conference, AIRWeb (Adversarial Information Retrieval on the Web), was created to bring together practitioners and researchers concerned with search engine optimization and related topics.
Google is the most popular spider-driven search engine. Its database currently has about 4 billion pages indexed and is known for finding the most relevant information. When Google spiders the Web, it finds sites by traveling through links. The more sites that link to you, the more important the engines believe your content to be. You should focus on getting many important sites to link to your site. You can do this in many ways: submit to online directories, exchange links with business partners and industry-related sites, or participate in Link Building.
You mentioned: "many times clients have already done this work. Ask them for copies of their market research reports when you start a project. It will save you a ton of time and effort!" We do this with most of our clients, like you said we have found that around 75% of the have some kind of Market research done, that saves you a lot of time and helps setting up the right SEO Strategy.