When starting a search engine optimization marketing campaign, you must not make any of these fatal seo mistakes.

1. Not using Title, Description or Keywords tags on every page of your website you want to succeed.  Or another issue is that you should not have duplicate Title or Description tags on your website. Every page should have completely unique meta tags.
2. Linking with Javascript within navigation. Unfortunately, depending on the Javascript code this could prohibit your success in the search engines. Either pages won’t get indexed or else link relevance won’t be passed on to your sub pages.
3. Creating a website that has important content more than 2 clicks from the home page.  Make sure to link from your home page (if possible) to content that is developed to improve your search engine rankings.
4. Creating a website entirely in flash without learning about the negatives associated with this.
5. Not updating your website regularly. I believe a website should be updated at a minimum of 1 time per month.  Once a week is even better.
6. Using image navigation without any link navigation.  There are benefits to using text navigation with good anchor text.
7. Promoting your competition’s ranking by linking to them without anything in return.
8. Functional problems with your website. For example Invalid Links, invalid Images, Invalid Sitemaps, Etc.
9. Not using search engine friendly URL’s.
10. Changing popular pages URL’s without using the benefits of a 301 redirect. Learn more at BigOak
11. Not working on either link building or link bait to improve your website’s link popularity.
12. Not creating a blog! I love WordPress, it is designed great for SEO to help demolish competition in the search engines.
13. Not branding your website as unique so people are inclined to link to you.
14. Linking to website’s that use illegal or bad seo practices - This is an easy way to run the risk of getting banned in the search engines.
15. Targeting the wrong keywords – Make sure that you focus on keywords you have researched and know will perform. Also understand your competition – if you are in a highly competitive field, expect 6 months to a year of really hard work to grab top rankings.
16. Not using your keywords in your content. Make sure to use your keywords within your content; however don’t use them too often or else you can hurt your rankings by keyword spamming.
17. Creating content only for the search engines! You should create content that visitors will enjoy as well. Sites that succeed long term offer something unique to their visitors that helps to spark visitor’s curiosity which will help to gain quality links.
18. Aiming for the hardest to obtain keyword from the start of a SEO campaign.  I have seen many website owners trying to obtain top rankings under major terms such as “cars” or “insurance”, then realizing that it’s nearly impossible without a large Internet marketing budget or years of daily and relentless branding, link building and link baiting.
19. Planning to succeed instantly! I like to look at my websites from the perspective that they won’t succeed for a long period of time. Then I try to prove myself wrong. This helps to keep myself from being let down if results aren’t instant! 
20. Last mistake is simple, many website owners give up on their website after putting so much in to them.  Ross Perot said it right, “Most people give up just when they’re about to achieve success. They quit on the one yard line. They give up at the last minute of the game one foot from a winning touchdown.”