1 – You didn’t spend time and effort carefully researching your keywords, using only popular keywords instead of long tail keywords, and failing to research what your competition is doing.
2 – Failing to check if your website is search engine friendly, and checking to see what penalties already exist for your website on various search engines.
3 – Failing to give every single page on your website a short (under 70 characters), unique title tag which includes keywords that are also embedded in that page’s content, and then including little to no text within the page’s content.
5 – Using a quick method to gain links, such as creating a link page, buying a service from someone offering 100 links for $10, using “link building” software, or using a link buying broker. These are invariably scams, and a waste of both time and money.