Ease Of Use
The most important thing about any website is that it's easy to use and suitable for the purpose for which it's designed. If you succeed in this respect it will also help to make it search-engine friendly. Well-written, easy-to-navigate pages with interesting information will get repeat visitors and satisfied customers. Some technologies, such as Adobe Flash, do not currently support SEO very well. These technologies should be evaluated on a case by case basis, before you decide to use them think "do they add anything to the site?". If the answer is no then it's best you don't use them.
"PageRank reflects our view of the importance of web pages by considering more than 500 million variables and 2 billion terms. Pages that we believe are important pages receive a higher PageRank and are more likely to appear at the top of the search results. PageRank also considers the importance of each page that casts a vote, as votes from some pages are considered to have greater value, thus giving the linked page greater value. We have always taken a pragmatic approach to help improve search quality and create useful products, and our technology uses the collective intelligence of the web to determine a page's importance." - Google
Content Is King
Regularly updated, well-written and relevant content is vital to your SEO campaign. If you can provide this then other websites will gradually give links to your site. A very popular but effective way of giving fresh content is blogs they are well received by search engines. Keywords are also vital for search engines, these are the words that you think customers will search for and for which you want to be found. Your content needs to describe your products and services and include the keywords, in order to sell them to your visitors and to help search engines index your site. Some decide that is best to pay to have content written professionally.