I’m a big fan of making lists and checking them twice, especially when it comes to SEO. There are far too many don’ts you want to know about when performing search engine optimization, or you might just shoot yourself in the SEO foot.
Although this isn’t an exhaustive list of search marketing mistakes, it covers what I believe to be the most important obstacles to steer clear of if you want your content to rank high in the search engines. Oh, and these don’ts aren’t listed in any particular order, since they’re all important.
1) Don’t use site submission or directory submission services or software unless they are highly recommended by an SEO expert, or allow user interaction during the process.
2) Don’t use too many keywords in your content (keyword stuffing), whether it’s the title, body, URL (file name), or meta tags. Use Keyword Density tools and don’t exceed 6% density.
3) Don’t submit your links to link farms, link exchanges, or similar sites or programs. Remember that one-way links into your website are better than reciprocal or paid links. A Beginner Mistake.
4) Don’t have too many external links (websites that aren’t yours), and make sure that when you do provide a link to another website, that it’s clean (not a spam site, banned, etc)
5) Don’t hide text on your website (using same/similar colored text as background, CSS displaying text outside visible area, or smaller text than the eye can see). This black-hat technique of packing excessive keywords into content that only search bots see was started years ago, and has long since been identified (caught) by search bots. This is a numbskull mistake.
6) Don’t use cloaking of any kind, or redirect methods. Develop your content so that both search engines and humans see the same stuff.
7) Don’t expect gateway or doorway pages to rank high in search engines.
8) Don’t use frames when constructing your website. If you find it convenient, for some purpose, to use frames on one or two pages, don’t expect them to rank high. And don’t use them on your domain root.
9) Always have at least 6 internal pages linking to each other so the search bots can crawl and associate them all with each other. This will give you maximum relevance, as long as keywords on each are similar. OK, so this isn’t a “don’t” or a “mistake”… unless of course, you don’t do it 
10) Don’t allow your server to go down or your sites to become inaccessible (a simple-to-avoid mistake). A good hosting company and programmer will insure your site is accessible by the search engines.
11) Don’t excessively repeat the same anchor text in external (or internal) links throughout your web pages. Your website/page could be viewed by the bots to be a link farm, or link spam. Use a 60%/40% rule.
12) Don’t use an excessive number of dynamic parameters in the URL. This usually happens when programs use query strings to invoke server side applications, causing “?”, “&”, “=” and other non-alpha numeric characters to appear. Search bots choke when they see these.
13) Don’t use different domains you own to point to other domains on the same IP address. Hosting plans allow you to host multiple domains on the same server, using the same IP. Doing this for the purpose of increasing incoming links from sites you own on the same IP could hurt you (or do nothing to help you).
14) Don’t have two or more web pages with duplicate content anywhere on the same domain. Big Mistake
15) Don’t let domains expire. This will have a negative impact on how the bots view your authority.
