Keep your site very content rich. Have a lot of pages.Update the site even twice a day if you have the time. Content is a golden word in SEO. If your content is Original then its a big plus. High ranking websites in google,yahoo and msn have a plethora of content.You can gain much on a poorly updated site.
Updating your site does not mean that you copy paste content from other sites.That will only push your rankings further down. Don't have any duplicate content. At the same time ,dont spam multiple content across the same website.
Clean URLs
Clean Search Engine Friendly URLs have always been known to help.
urls like domain.com/articles.php?id=344 are not bad.
But domain.com/articles/name-of-article/344.html is a great option.
Have the Web User in Mind
Build your website having the general layman who spends time on your website in mind. Having a site with good accessibility always has a good future.
No to excessive out bound links
Dont have too many links on a single page. Instead split your content into sections/categories. Too many outbound links are not good for SE rankings as well as visitors. It may look like a link farm or directory.
Never link to illegal sites
Linking to sites that are not doing lawfull stuff may get your site blacklisted.Stay away from such sites even though you might loose some bucks.
No spyware / adware
Never make your site a home for spyware and adware. Try to keep your site clean and easy to use.
Never ever try to hide text in a webpage to a user, and show it to search engines.Search Engines are smart these days and are not text only anymore. They even give importanct to the graphical information on the site.
Reliable Web Host
Get a webhost which has more than 99.5% uptime. Its a total waste if you have a fantastic website but its not online