In a nutshell page performance is widely understood as the page load time from the users' perspective, so below are some steps that might improve a page's performance.

Use sprite images whenever possible, try to group small images commonly used in a single file to be requested just once. See how Google uses sprites in Google Maps to make one request instead of one for each small image. See a sprite from Google Maps

Javascripts should be at the bottom of the page, instead of in the head as we use to see out there;

Ensure parallel requests of your JS and CSS files. In order to force the browser to do that, you can optimize the order you include resources in your page. This item can generate its own blog post or even a book so I prefer to suggest you a really good reading about it.

Compress images whenever possible, it makes a difference;

Browser Caching is also very import to be set for static resources like JS and CSS files, images, PDFs and HTML. Caching is set in the HTTP header by informing browsers the expiry date or maximum age. Then browsers can load the last downloaded resource from the cache instead of request it again.