To help you prevent typical flaws webmasters encounter regarding SEO (Search engine optimization), Google made a video detailing 5 frequent mistakes.
Here is the video :

If you are short on time, here is the gist:
Stay away from these typical mistakes
1. Do not imagine that a website really should rank #1 with no knowledge of why it is important to searchers or visitors (and much better compared to competitors :) )
2. Be careful of establishing SEO-related targets without ensuring they are aligned correctly with your organization’s general goals seo mistakes by seo companyand also the desired goals of other business units of your company.
3. Stay away from employing a hack instead of researching latest features or guidelines that could make simpler development (e.g., modifying the timestamp on an URL so it is spidered more rapidly rather than easily posting the URL viaFetch as Googlebot )
4. Consider investing less time worrying about the hottest “trick” to improve your search rankings and rather concentrate on the basic tasks which will bring long lasting site visitors.
5. Try to be nimble instead of showcase an environment in which the infrastructure and/or techniques make enhancing your website, or perhaps testing feasible enhancements, tough.
If you working in a professional SEO company or If you are trying to optimize your website then you should avoid these common mistakes.
For More information please visit Google webmaster central blog