1. Google watches code. Keep it clean, like Saf said. Using CSS and keeping tables for tabular data. Use simple metadata that is related to your website. If you try anything tricky, like a page worth of metadata, Google doesn't like it and will bump you down. Google also does not like frames or Flash. Keep any text as TEXT so Google can read it easily.
2. Content. It's important. Be clear, don't use lots of acronyms. Have good links to quality websites. Google looks at the quality of links it finds on your page to help judge it's quality.
3. Template text. Take key text, like the name of your company, or a box with a description or tag line, and have it on each page. (This is usually accomplished with a header and footer) Google will notice that it is part of your site, and weight it accordingly.
4. Load time. Make sure your site loads FAST. Just like users don't want to wait, Google doesn't like waiting. Ensure that your graphics are light weight and of good quality, or Google may start marking you down.
5. URL's. Keep them short, simple, use English. index.php?page=home will produce much better results than index.php?id=001.
Does that help a bit?
Note: I'm not an expert at SEO, per se, but I offer it as a professional service from my company, and I have had the opportunity to talk to the Google reps through my university.
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