Rand Fishkin from SEOmoz has compiled a list of 93 factors that could have an effect on your search engine rankings. Some of these are common knowledge such as the fact that title tags are one of the most important elements. Others may come across as speculative such as the use of header tags (H1), bold and other visual tags. And then there are some that seem to change all the time such as the value of links.

Using a graphical symbol scale, Rand assigns a level of importance for each factor, those being Exceptional Importance, High Importance, Moderate Importance & Low Importance. He also prefaces the list by stating that these factors can influence a web document's rank at the major search engines (Yahoo!, MSN, Google & AskJeeves) for a particular term or phrase and that it is impossible to say for certain which of these items affects which search engine or how important the factors are individually.

The list is broken into five categories: 1.) In-Document Factors Affecting Ranking, 2.) Site Factors Affecting the Value of Hosted Documents, 3.) Factors Affecting the Value of a Link, 4.) URL, Technical, Hosting & Server Side Factors and 5.) Detrimental Ranking Factors. I especially like the detail that is given to each factor making it much more of a guide as opposed to a simple list. Kudos to Rand and those who assisted him in compiling this most comprehensive list.