This seems to be a major issue for most people. Please note this tutorial was made on 4-10 and some of the examples may change in the future if the webmaster updates his or her website. Most people know how to navigate through the Title and Meta tags, how to create properly optimized content and navigation that flows. What most people do not understand is proper indexation and duplication/similar/overlapping content. What I say duplicate content I am referring to exact copies of the same page on the same website. You can also have offpage duplicate content caused by people stealing your content or you stealing theirs. When I say similar content, I am referring to having two articles like "How to make money online" and "Making Money Online". When I say overlapping content, I am referring to having partially duplicate content appear on the page. The best example is an except. Now a certain amount if duplicate/similar/overlapping content appears to be tolerate. It because a problem when there is an abundance of them and this will make your site rank lower. Having several of these low quality pages will hurt you. I randomly searched for the term make money online and found this EMD. I have no idea who owns this website, so they will serve as an example: http://makemoneyonline.biz/ They currently rank about #45. Now this website is going to have a difficult time climbing on to page 1 in my opinion. Here are several reasons why. If you visit Google.com and do site:makemoneyonline.biz you will start to notice a few problems. 1. This tag page is serving up overlapping content. This person has it in the form of an except, but many tag pages will display the full article. http://makemoneyonline.biz/tag/twitter/ You will also notice the two pages have somewhat similar ideas for their content. http://makemoneyonline.biz/blogging/using-twitter-to-attract-readers-to-your-blog/ http://makemoneyonline.biz/blogging/attract-followers-on-twitter/ 2. I wouldn't consider these tag pages high quality pages and this could also be hurting the website. http://makemoneyonline.biz/tag/nofollow/ http://makemoneyonline.biz/tag/exact-match/ 3. Also notice on many of the article pages there are two ads above the fold. Google Adsense messages will tell you to put 3 or more ads on the website because you're missing out on potential revenue. What they didn't tell you is too many ads seems to decrease your onpage SEO score. In general one ad above the fold is fine and then a second one is fine lower as long as you have 500-1000 words on the page. http://makemoneyonline.biz/seo/nofollow/ 4. Here is an example of overlapping content created by two tag pages with the same excerpt. http://makemoneyonline.biz/tag/create/ http://makemoneyonline.biz/tag/directory/ 5. Here is an example of an empty page created by the archives. http://makemoneyonline.biz/archives/ 6. Category and Tag Pages with some overlapping content. Google could easily be confused about which page should rank about SEO. http://makemoneyonline.biz/seo/ http://makemoneyonline.biz/tag/seo/ 7. Blog Post Pages creating overlapping content with tag pages. http://makemoneyonline.biz/seo/page/6/ http://makemoneyonline.biz/seo/page/7/ 8. Duplicate Tag Page with a page 2 http://makemoneyonline.biz/tag/blogging-2/page/2/ http://makemoneyonline.biz/tag/affiliate-2/page/2/ 9. Author Page creating overlapping content. http://makemoneyonline.biz/author/mmobiz/ So how can this problem be solved? In general, use your Wordpress SEO plugin and noindex, nofollow category/tag/author pages unless you really know what you are doing. I see this problem every day and people blame it on link building. What actually happens is since Panda 1.0 Google has been holding sites in cue. Then when they release an update they penalize all of these sites for onpage SEO. Another common thing I see is someone builds links and then they drop. This is because the Googlebot is coming back to the website and evaluating the website again and then notices all of the poblems.