1. Do not link to non-trusted, low quality websites. If its absolutely necessary, use the nofollow tags.
2. Do not over emphasize keywords on articles. Keyword density is an old SEO metric. Get over it.
3. Do not over load pages with Ads/Scripts/Template scripts that will increase page load time.
4. Do not copy content from other websites.
5. Do not leave an unnatural number of broken links / pages on your website.
6. Do not use hidden keywords in pages.
7. Do not use cloaking.