Matt Cutts' Top 5 mistakes made by Webmasters
1. Not making the website crawlable or not having a site at all. Test crawlablility with a text browser.
2. Include the right words on the page. Keywords People are actually going to use. Think about what the user is going to type and include those words. Do not just use "Mt Everest Evaluation" you want to say "How High is Mt Everest" because people are going to type, "How High is Mt Everest”.
3. Not just link building think about Compelling content and Marketing. As soon as you think my job is to build links. You’re cutting off a lot of avenues. Think compelling content & marketing, more, more, and more.
4. Title and Description of your really important pages, Really should pay attention to your home page, if its bookmarked, are you going to be able to have users find later on find exactly what it was... And your Description can sometimes determine what determines what shows in you snippet, and that determines whether people will be enticed to click it.
5. Not using webmaster Resources’, Documents, forums, videos, http://www.google.com/webmaster