Getting quality back links to your site is a well known tactic to improve search engine positioning. However if the back links are created too quickly you can get penalised for over optimising the keywords in your back link campaign. Google has an over optimisation penalty which seems have been intensified in the latest Panda Update. If you have seen pages disappear with this update them this is one of the areas you should be looking into. Click here for more information about better ranking after the Google Panda update.
Getting Links from other sites, blogs and directories
Sites should obtain back-links slowly so that they appear natural to Google. Obtaining too many back links over a short period of time can be seen by Google as a link spike.
To avoid penalties for over optimisation, links should be added naturally over the year. The analysis of the number of links gained over time is called link velocity, what you are aiming for is a steady increase in backlinks with no obvious peaks
Anchor Text and Keywords
Another way you can fall into the over optimisation penalty trap is building too many backlinks with the same anchor text. Make sure you use varied anchor text, a link campaign which just contains the same keyword backlinks could appear to Google as an unnatural link buying campaign which can result in a penalty.