In the past before html5 we normally only used one h1 per page but now that html5 allows for more than one h1 you still need to be conservative when using them
At the very least use h2 for sub headers. You might not need to go lower but use h3,h4,h5,h6 whenever necessary.
Strong and Emphasis
Use strong and emphasis tags to show importance (should be less important than what is included in heading tags)
Include keywords in alt tags whenever possible but remember you are still describing the image for 508
Naming links correctly not only helps SERP it will also help you to track the flow of traffic as the users moves from pages to page. The page names are listed in Google Analytics both under Content and Visitor Flow.
Create meaningful urls with keywords whenever possible
Hyphens in page file names not underscore or camelCase. Google has recently (August 2010) announced that for the moment they will not recognize underscore as separating words