There are some common mistakes those are unknowingly done those are detrimental for SEO of a website. It is fact, no one wants to kill own website. Everybody wants traffic; more and more. Google will send you more and more if you strictly check these things which are very commonly done mistakes.
Graphical header and HTML title tag
If you are using WordPress with a good SEO optimized theme hosted on a Linux server (Windows server will not support certain permalink structure), you will not face it. The theme’s panel will give you option to choose between dynamic text (that is set from WordPress settings it self or might be custom theme’s one) and image header. When you choose image header, it automatically add a title meta tag. So, you do not have to worry about, if you have set the right post taxonomy selected.
But, for other often the website designer creates a graphical header, which is same width as of the body and usually containing the company logo, name and other things. It is very important and highly important position, which can be used for other purposes, for example, to place SEO – wise interesting text with keywords. Google or any other search engines can not see the pictures and these pictures has no way to put alt attribute to it.
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No or very badly structured navigation menu
If your website has 20 posts, it should have a proper hard coded HTML navigation with or without CSS and JQuery fancy things (you can our navigation).
Internal links on the website navigation must also include some keywords, it will provide an advantage when ranking sites. If the navigation menu is presented in the form of graphics to create a more attractive (and destructive) menu, then search engines will not be able to take into account the links hierarchy.
- Header navigation is the best.
- A logical hierarchy is the best. What is a logical hierarchy? Our download section contains all posts of the sub-categories of download section. Some SEO philosophers say it is bad to add one post in more than one category. This is totally wrong as their logic is wrong. Google understands from the Navigation, which is a category and which is a sub category. It is same like classification of animals and plants. For example, class Insecta belongs to: Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Hexapoda
Class: Insecta
So, Phylum Arthopoda contains Trilobitomorpha, Chelicerata, Myriapoda, Crustacea (we love to eat them) and Hexapoda (that is where our Insecta belongs to). - Hard coded HTML list must appear in the source code.
- Having sub, sub-sub should be considered when posts are of different types and more than 50. Because, (to Google) it establishes the web-master is a wise person and have arranged the posts as much as scientifically as possible.
- Never try to link external websites from header navigation, even your sub domain. It is dangerous for SERP. Those who read our posts will understand the logic.
In some cases, the navigation of the website is carried out fully by using flash. Keep in mind that search engines will not read those scripts. So, the link defined by the script will not be available to search engines and search engine robots will not index it.
Session identifier
Many developers use the session id. This assigns each visitor at the entrance to a resource unique parameter that is added to the addresses of visited pages of the resource. The use of session id enables more convenient to carry and handle statistics about the behavior of web site visitors and may be used for other purposes.
But for a robot it is a new page. When entering the search robot gets a new identity and consequently visiting the same page will perceive them as totally new. No knowledge of rocket science is needed to understand what will happen. Search engines use algorithms of mirrors with duplicate content, and as a result of those pages will still be indexed, but the index of such sites is difficult and often leads to incorrect operation of the website.
No tag cloud
A nicely well thought tag cloud is always good for SEO of the website. Put near footer but not on the footer.
Too much nofollow to categories, tags
The bad habit of using nofollow is increasing. Some gurus says the mantra of adding nofollow to Tags, Categories etc. It is good if you have 200 posts of totally different type in your blog, when you have 200 posts of same tags or categories, it is bad. Sitelinks are considered SEO wise an aristocrat thing, we got 6 sitelinks within 6 months of the launch of this website (4 are appearing now in Google search). The other sitelinks those will appear later (we can predict for sure) are SEO and WordPress :

Other bad habits
Adding no alt attribute to images, no moderation of comments, adding chunks of keywords in meta keywords field. Example of junk keywords for this posts are: Google,Google search,Google searches,searches,sitlelink,site links,site link,sitelinks,navigation,navigations, (and all possible spelling mistakes). Get rid of this bad habit. Google does not depend on keywords, but mark as bad spam effort if you use such junk words.