Exactly how Google works out which sites to list first are unknown but there are a number factors that are known to influence it.
This score ranging from 0 to 10 has made Google billions of dollars. By giving a web site a score based on the Page Rank of all the sites linking to it, Google created a quick method of gauging a web site’s quality. Unfortunately it was also easy to trick or manipulate and so nowadays, PR has a lot smaller influence on Google’s results.
How many external links (links from other domains) to yours is probably the single most important factor involved. However having more that your competitors does not guarantee you the number one spot because of the interaction between links and keywords.
How often a keyword appears on page certainly is a factor but no one can decide how important it is. Some SEO Experts say it is vital to have a density of x%, other say it doesn’t matter as longs the keyword is used a few times. My experience is that if you follow the Once Per Paragraph Rule, you will get the ideal amount of keywords in your content.
There are four keyword-in techniques: using the keyword in the domain name; using the keyword in the <Title> tag; using the keyword in the “keywords” attribute of the <Meta>; and using the keyword in the “Description” attribute of the <Meta>. These give only a marginal advantage in Google but that slight edge may be all that is separating your site from your competitors.
New domains are penalised by Google. It prefers older, more established web sites because spam web site come and go very fast. This handicap for new sites lasts no more than a year and it is certainly a not major problem. The web can respond very quickly to events and brand-new web sites can be at the cutting edge. Google recognises this so the penalty for being a new domain is very small.
New pages or pages that have been recently updated are favoured by Google. So keep in mind the Three U’s: Useful, Unique and Up-To-Date.
Too much of a good thing is bad for you and likewise packing your web page with a keyword is bad for your web site. Use a keyword too much and Google will think you are spam. How much is too much? No one knows but Google and they are not saying so just be sensible and remember to ask yourself ‘Does my web page look like Spam?’.
You can see how these factors effect real world examples in "Britney Spears", "Sex" and "SEO".
Chris Tregenza runs a variety of web sites including MiceLife, writes free seo articles and a SEO Blog
Better search engine placement through article writing.