Based on this very old article on the ranking factors that Google uses, I thought it was due an update and an order to the top 100 ranking factors that you need to worry about. To be clear, this list is based on the order of things we would worry about with a new site we were asked to optimise. It basically ranks the factors from easiest to deal with right now, through the things you need to think about in the medium term to the least important thing you should worry about.

1. Server reliability / uptime. More uptime is good. Google will crawl your site regularly to check.
2. Site age. The older the domain, the better.
3. Site top level domain. .com>.info. local domains are better than .com
4. Keyword accuracy in the domain.More succinct and accurate the better
5. Brand term in domain name. You score more points long term by having a brand
6. Geo-targeting settings in Google Webmaster Tools
7. URL structure (pretty URLS). Go for /blog/something/pretty rather than /index.aspx?something=312312
8. HTML errors. Less errors are better. Test regularly
9. Webpage structure (reviews, comments etc are better)
10. Website accessibility (mobile, alt text etc). Google sorts results for browser
11. Is your content shared on Google+
12. Does the business have a Google+ page?
13. Does your website have location based information?
14. Are you using rich snippets for author information?
15. Use of canonical URLs.
16. Website Robots.txt file content
17. Overall site size (number of pages). More is better
18. Overall site update frequency. More is better
19. Amount of content (text versus HTML);
20. Unlinked content density (links versus text);
21. Content topicality / newness. Recency of posting is tracked
22. Has a user recently visited you? Then you will rank well on their browser
23. Content variety (videos, images, documents)
24. Content variety images sizes, content sizes
25. Word Variance (ie no keyword stuffing)
26. How often the listing is clicked within the SERPs. You can’t control this, but your page description should be interesting enough to encourage people to click.
27. Phrase Based relevance (3 + 4 word combination variance)
28. Banned keywords usage
29. Rampant mis-spelling of words, bad grammar, and 10,000 word screeds without punctuation;
30. Number of internal links to page;
31. Number  of internal links to page from content (instead of navigation bar, breadcrumbs, etc);
32. Age of the site since it was first discovered by Google
33. XML Sitemap
34. Link profile diversity.  Get links from a range of sites using a range of anchor text.
35. On-page trust flags (Contact info Privacy policy, TOS, and similar);
36. Page meta Robots tags;
37. Content duplication across site. Avoid it at all costs
38. Page load time. Reduce this by using images that are appropriate for the web
39. Keywords in the title of a page;
40. Keywords in the beginning of page title;
41. Keywords in Alt tags;
42. Keywords in anchor text of internal links (internal anchor text);
43. Keywords in bold and italic text
44. Keywords in the beginning of the body text;
45. Keywords in body text;
46. Keyword synonyms relating to theme of page/site;
47. Keywords in filenames;
48. Keywords in URL;
49. Number of outbound links
50. Quality of pages the site links in
51. Links to bad neighbourhoods
52. Relevancy of outbound links
53. Relevancy of sites linking in;
54. Relevancy of pages linking in;
55. Quality of sites linking in;
56. Quality of web page linking in;
57. Backlinks from the same groups of sites
58. Anchor text diversity
59. Different IP addresses of linking sites
60. Geographical diversity
61. Backlinks from bad neighborhoods
62. Reciprocal links ratio.
63. Social media links ratio. Reddit.com etc have very good value for good content
64. Backlinks trends and patterns. Sudden spikes in backlinks of one class are bad.
65. Citations in Wikipedia and Dmoz;
66. Business citations in yellow pages.
67. Backlink profile historical records (ever caught for link buying/selling, etc);
68. Backlinks from social bookmarking sites
69. Authority of TLD of link
70. Authority of a domain linking in
71. Authority of a page linking in
72. Location of a link
73. Anchor text of a link
74. Title attribute of a link
75. Content around link
76. Volume of content around link
77. Bounce rate of site
78. Vistor Bounces and then blocks your website
79. Keyword over usage / Keyword stuffing
80. Link buying flag
81. Link selling flag
82. Spamming records (comment, forums, other link spam)
83. Cloaking
84. Hidden Text
85. Duplicate Content (external duplication)
86. History of past penalties for this domain
87. Past hackers’ attacks records
88. Malicious content (possibly added by hackers).  Make sure your site is protected from hackers.
89. Registration with Google Webmaster Tools;
90. System update (esp. WordPress). Keep your software up to date
91. Google Places registration. 
92. Google Places authority citations