1) Optimizing the wrong keywords
a) Selecting keywords that bring untargeted traffic
b) Choosing highly competitive keywords
2) Overstuffing meta keywords tag
3) Keyword repetition
4) Creating multiple similar doorway pages
5) Use of hidden text
6) Creating graphical webpages
7) Page Cloaking
8) Too many page submissions per day
9) Using submission tools that are automated
10) Dedicating too much time for search engine ranking
To know more about this subject, please visit –
http://www.pharm-education.com/2009/11/seo-mistakes-to-avoid-during-blogging.html

