Almost all important things said, I may add a few little uncommon things:
1. Be careful with metatags, make sure they are different on EVERY PAGE or just use none...or you got a problem faster than you can say "supplemental index"...same goes for the page title, it should be at least partly unique on every page.
2. Use different IP adresses, the more the better, although established sites will take a little hit when changing the IP, they recover fast. Just a security measure if google kicks a domain, all on that IP get some negative "points"...the reason why most people on hosts that share IPs for dozens of clients often work off their asses without getting good results.
3. Do not use any domain privacy services, so far it's just a rumor that it hurts your ranking, but google filed some patent that involves a whois check for domains...
4. Read
http://www.mattcutts.com/blog/type/googleseo/ from time to time.