Search Engine Ranking Influences
Links from existing web sites that the search engines already see as "important" or popular really helps. With Google for example, if you have a newer unpopular site and you get a few links from very popular sites, your ranking will increase. The following also influence ranking from what I have experienced:
1) Volume of incoming links
2) Relevancy of incoming links
3) Proper code / no broken links
4) Site content (this probably should be #1)
5) META tags
6) Age of domain (seniority)
7) Uptime
8) Overall optimization
9) Loadtime
10) Periodic submission
I'm sure there are more to mention, but I hope this is helpful.