* Placing keywords where spiders can find them easily – Your keywords will tell the search engines what each page on your is about which in turn helps them to determine the page's relevance to each keyword. Good locations for keywords include title tags, meta descriptions, alt text, headlines, and in the text on the page.
* Spider friendly navigation – The easier it is for search engine spiders to navigate your site, the easier it will be for them to gather information about your site. Building a search engine friendly site map can go a long way toward assisting the spiders get around your site.
* Use descriptive terms in your URLs as opposed to sequences of numbers, letters, and symbols - Descriptive terms make it easy for the search engines to determine what is on the page which can increase your visibility.
* Optimize images – Adding alt text is often overlooked but it's a great way to add keyword related content to a page which will get picked up by the search engines.
There is a lot more to search engine friendly website design but these tips are a great starting point.