External factors’ peculiarity is that they are very difficult to change (in some cases this is impossible at all). One of the main factors is the number of links that lead to your site.
Search engines count not only general links’ amount but their quality too. Links received from authoritative sites (for example, New York Times) have greater weight. Links received from public institutions, non commercial organizations and university sites are able to positively influence the site’s location in the SERPs.
There are many parameters when evaluating the links search engines count: what keywords and phrases they include, whether they are similar with the subject of a page they are placed on and a page they point to. Other links placed around your links are also counted. If the link is located in one block with other links, search engines can considers them as paid ones. That’s why it’s better to place the links in offers.
The links also have to be natural. Participation in link exchanges, link spam and other means of promotion can lead to punishment – penalty.
When optimizing new sites, don’t forget about the sandbox effect.
Links growth has to be gradual: sharp surges of links growth can negatively influence the site’s ranking.