In many regards,  search engine optimization is a black art because there is not a set of definitive rules to follow, therefore,  much is left to both interpretation and emotion. Emotive decision factors are never a good thing!  Google publish a set of best practice guidelines but there are many nuances above and beyond the guidelines that define them as that guidelines not rules.. However, publishes a list of the top SEO factors as assessed by a panel of experts and below is the top five from their overiew, for search marketers this is an invaluable report. Read the full report here What is interesting about this survey is that even that panel of experts cannot agree and where consensus is not achieved a contentious factor is assigned. This is good reading for the search marketer.

  1. Keyword Focused Anchor Text from External Links

    73% very high importance

  2. External Link Popularity (quantity/quality of external links)

    71% very high importance

  3. Diversity of Link Sources (links from many unique root domains)

    67% very high importance

  4. Keyword Use Anywhere in the Title Tag

    66% very high importance

  5. Trustworthiness of the Domain Based on Link Distance from Trusted Domains (e.g. TrustRank, Domain mozTrust, etc.)

    66% very high importance