SEO - Design & Layout
A web site design and layout gives first impression about your site. There are sites which are too fancy and regular net surfers will just reach on those sites and will come out even without creating a single click.
Search Engines are very smart but after all they are software and not human being who will read the content of their interest. If you make your site too complicated then Search Engine would not be able to parse the content of your site properly and finally indexing would not be efficient which will result in a low rank.
The actual page content should have a keyword density of about 10% and should weigh in at about 200 words - but there are as many opinions about this as there are SEO experts. Some say keyword density should be 5% and some say it should be 20%. 10% works for me.
Here are few guidelines which should be considered while designing a web page.
You should have more text content than HTML elements.
No frames. They are the enemies of Search Engines and Search Engines are Enemies of Frames.
No ads if possible. Because most of the ads uses Java Script which is not advised to be used.
Nothing that does not fit perfectly into the page topic; There should be no doubt in the search engine's mind (or in he user's mind) what your page is about.
No unnecessary directories. Keep your files as close to the root as possible.
No fancy stuff (Flash, Splash, Animated Gifs, Rollovers etc.) unless absolutely necessary.