Here I have listed out some comman top SEO mistakes
Targeting With Wrong keywords
Wrong keyword targeting is worse mistake many people make, even experienced SEO specialist make it, we should choose keywords that the average user type to search, for example if you have a Employment site, you might choose that “Employment board” does not work here, even it has the “employment” keyword, while “Job board”,”Fresher Jobs” works like a charm. Choosing the right keywords is the first step for doing good SEO. you can also use some keyword suggestion tools for this, it will help you to find keywords that are good for you site.
Flash websites are might be attractive but Search engine won’t search them, if you really want your site is flash based and you want search engines to love it, do an html version. Search engines don’t like flash websites because a spider can’t read flash content and index it.
Ignoring the Title tag
This is also very common mistake, Title tag is one of the most important area to have a keyword, because the text in your title tag shows in the search engine result as your page title and also help you in optimization.
Meta Tags Concentrating
Many people seem to think SEO is about getting meta keywords and description, but its not true. You can create your meta keywords and description but don’t think to rank well only because of this.
Using Images for Headings
Usually webmaster think that an image looks better than text for headings. Its true, but text links and text headings are more SEO friendly.
Keywords in URLs
Many Webmaster knows that how important keywords in the URL is. Avoid Dynamic page URLs as possible. It is possible to rank high even without keywords in the URL but if you have keywords in URL, this gives you additional value over you competitors. Keywords in URLs more important for MSN and Yahoo Search, so don’t forget to having keywords in URLs. if are you the wordpress blogger, read it “How to Optimize Search Engines friendly URL in wordpress blog?”
Yes, It is true more backlinks are always better, but because of this web masters resort to link farms, forums, Spam etc., which could lead to getting their website banned. actually you need a quality backlinks.