Every SEO "expert" will give you an array of different answers about what you need to do when it comes to implementing some sort of search engine optimization strategy.
But all the various techniques, suggestions, and urban-legends boil down to three main tactics. These are as follows:
(1) Link Cultivation. Ensuring that you have a large number of high quality (meaning: objective and credible), third-party links to your site. To achieve this, as a practical matter, your site needs to have usable, high quality, and useful content.
If there's not good content, why does anyone want to link to your site?
(2) Site Structure. Making sure your site is easy to navigate and that links between pages are clear and easy to understand goes a long way toward making your site "search-worthy".
Also, making sure that key elements of your site are in readable text (instead of Flash, or graphic images) is very important.
(3) Keywords. You have to do your homework. For your business and market what are the optimal keywords to find your site? You can find these using various tools available from folks like Overture, Wordtracker, or Google, but wherever you get them, use them on your site and use them prominently.
Search engine optimization requires optimum keyword-rich copywriting and page-tagging. Do ensure that the keywords you choose are appropriate for your market. If you select inappropriate keywords, your site will attract unqualified and irrelevant users.