SEO Donts

Outgoing links
Keep the outgoing links under 100 per page. Too many outgoing links will affect your page ranking.

Flash and Graphics
Search engines won't read flash movies and images so don't over-use either, and be sure each page has enough content to allow the SE's to decide what the page is about. Try to use keywords in "alt" tag for an image.

JavaScript links
Googlebot is not able to follow JavaScript links. If you use them just make sure you have alternative navigation using HTML links.

Single pixel links
Single pixel links are invisible for humans. These links is an attempt to manipulate search engines. So avoid such links.

Sessions
Google won't accept session cookies and will try avoiding URL based sessions.Use fewer parameters in you dynamic URLs and avoid use “id” parameter as Googlebot may think that is session ID.

Hidden text
You will be identified as spammer and banned from SERP’s, don’t use hidden text.

302 redirects
When a URL returns a 302 redirect, it means that the owner of this link asks users to continue to use this address as the redirect could be modified at some later time. The challenge for search engines is to allocate the content to the appropriate address. So try to avoid 302 redirects. When a page has been moved to a permanent new address, Google recommends to use a 301 redirect

One URL and differing content
Search engines get confused what the actual content of the page is. Try to avoid such pages

Cloaking
Cloaking is a search engine optimization method where you serve highly optimized page version to robots and a regular page to your visitors.These cloaked pages will not be indexed.

Duplicate content
Same content on several pages on the site can affect your PR.

Frames
Frames are very, very bad for SEO. Try to avoid them.

Dynamic URLs
Spiders prefer static URLs.Long dynamic URLs are really bad for SEO.Rewrite dynamic URLs to something more SEO-friendly.

Bad navigation
Your website must have a simple navigation. Make sure that Googlebot will be able to crawl your entire site.Most suitable place for navigation links are on the top of the pages since this makes it easy for your visitors and Googlebot to navigate through your site.

Submitting to FFA websites
Dont submit your website to free for all networks and pages (FFA). They may promise to provide a top ranking for your website, in which this will actually have a negative effect to your PR .

Automated link exchange networks
Don’t sign up to any automated link exchange networks