Use MS Visual Studio 2010 which helps
you in optimizing your .NET code for
better performance.
CSS sprites are very useful when you
have a lot of images in background.
Compress the contents of JavaScript
files using gZip compresser and CSS
file by removing white spaces and
comments.
Avoid HTML comments as they are
visible to client side by "View
Source" option in browser, which
will also reduce the file size.
Put most of the unnecessary
JavaScript at the bottom of the page.
For better performance dynamically
load the JavaScript references after
loading contents on your page.