From the start of whole seo game, a debate is going on the factors considered by search engines in a site to rank it a proper position. It is what people claim to know but search engines are strict enough to their policies as no one could describe it all in its original sense. Still some seo gurus have found out few factors which should be focused by webmasters to gain good rankings in search engines.

Out of these factors positive ones which should be followed are:
Use of Meta tags and especially the presence of keyword in title
Use of alt tags and anchor text for inbound and incoming links
Age of site and its link popularity

Some negative factors which should be avoided are:
Duplicate content with already existing sites
Extensive linking to low quality sites (spam linking)
Focus on making seo targeted sits rather than customer friendly sites