Tips for improved performance

Keep the number of HTTP requests to a minimum
On the initial load only use JavaScript to add event listeners
When using Web Fonts keep in mind that users might not download the font because of bandwith issues, so make sure the fallback looks good

What about new APIs and features in browsers?

Technology such as WebGL or new options in CSS can be used, but you must make sure that it has a built in fallback for legacy browsers.