Here is a list of 10 of the worst mistakes you could make, that at worst could get your website banned, and if you are lucky, their implementation would just impede your success in achieving higher organic search engine positions.
1. Keyword stuffing. Needlessly stuffing your keywords on your web pages will sound nonsense not only to your human visitors but also the search engines. This tactic could actually harm your rankings.
2. Don't move or remove a popular page. By keeping a regular eye on your website statistics you should be aware of your current popular pages. If you need to reorganise your site structure then remember to 301 redirect via .htaccess from the old location to the new one.
3. Do not use images in navigation. For the moment at least images mean nothing to search engines. It is therefore preferable to use text links in your navigation web designer use CSS for styling. If there is no getting away from from using images then do not forget to use the ALT attribute and put relevant (keywords) text in there.
4. Do not use an incorrect robot.txt file. An incorrect robot.txt file can totally stop search engine traffic. A single incorrect command in this file can block an entire folder. If you need to use a robot.txt file ensure that you do not block the search engines when you do not mean to.
5. Do not procrastinate. SEO begins at the initial website structure planning stage and never ends. There may be lots of work involved but the sooner you start the sooner you will reap the rewards.
6. Do not exchange links with everyone. Outgoing links to bad neighborhood, unrelated or banned sites will certainly not help your SERPs.
7. It can be easy to foret the human visitors, make sure you do not. Do not neglect your human visitors, remember that eventually it's the human web designer who are going to do business with you, so keep them first. Reputed SEO consultants believe that websites that are human-friendly are search-engine-friendly automatically.
8. Using analytical tools will help. Analytics tools like Google Analytics and others help you know how much traffic you are getting from various sources including search engines. They also tell you which are your popular pages and for what keywords you attract maximum number of visitors.
9. Do not focus on too few keywords. My last point discussed longtail keywords. Your main keywords may get you lots of traffic from few sources, but your long tail keywords can get you small chunks of traffic from many sources
10. Do not be impatient. It can take a while to see good results, so be patient. For instance it may take more than 5 months for your website to even start appearing in the search results. That's why it is a good idea to start sooner rather than later.