There's not really a specific quantity of back links as Google's formula uses weighted factors. Essentially, you would like sites which are relatively comparable subject as yours but possess a greater page ranking to backlink to your website. This determines your site being an authority. So, each link includes a different value for your ranking. Now, one way backlinks are the most useful. Buying and selling links isn't a sound practice as Google can easily see reciprocal links.
Lacking back links, submissions are King if this involves page ranking. The greater your articles is, that's, that contains keyword wealthy text without over stuffing is nice.
