Here is the list of the most influential factors on SEO. Sorted by Priority:

1 * HIGH * Title Tag - Description of Website
2 * HIGH * Domain Name
3 * HIGH * H1 tag or first headline of document content
4 * MID * Description Meta Tag
5 * MID * Keyword Meta Tag (Not emphasized by Google, but needed for Yahoo and Bing)
6 * MID * Body of Text Italic
7 * MID * Body Of Text Bolded
8 * MID * Body of text generic
9 * LOW * Keyword Density 5-20%
10 * HIGH * Latent Symantec Indexing - Related words on topic
11 * MID * Sub headlines H2, H3 etc
12 * MID * Phrase order within the page
13 * MID * Keyword proximity of eachother
14 * MID * Font size +2 for sub-topics
15 * MID * Keywords within your alt text of image descriptions
16 * HIGH * Keyword early within the page
17 * HIGH * Keyword in links to other pages (on or off site)
18 * HIGH * Quality of other sites you link to
19 * HIGH * Topic of other sites you link to
20 * HIGH * Tree like structure of navigation
21 * MID * Internal links valid?
22 * HIGH * Number of links on the page itself (less is better)
23 * MID * Domain names you link to (Gov is best, then .edu, .org etc..)
24 * LOW * Web page size (IE: under 100k)
25 * HIGH * Hyphens in domain or file names more than 4 is bad
26 * MID * Page changing, more often updated pages prefered
27 * HIGH * Domain age
28 * MID * Page itself Age
29 * MID * Sites with more internal pages (IE: over 100 internal pages)
30 * MID * Page Theme
31 * MID * Frequency of updates themselves
32 * HIGH * Interesting title tag - Gets more SERP clicks than another
33 * MID * Appropriate links between itself and other pages
34 * LOW * Having a robots.txt
35 * LOW * Stating a physical address (Trust)
36 * LOW * Stating a support email address
37 * LOW * Describing every image
38 * LOW * Naming the images themselves thematically
39 * MID * Keyword in name of page itself
40 * MID * Document within a related folder or subdomain