Web optimization includes server side optimization, as well as CSS, Javascript, Images, and CMS.
The best way to optimize server-side is:
- choose a decent web host,
- host your images and static scripts separately,
- compress your content,
- minimize redirect, and
- reduce DNS lookups.
For CSS, Javascript, and Images optimization: merge multiple JavaScript into one, compress javascript and CSS, customize header expiry/caching, off-load them on another server, optimize images by not scaling them, keep CSS short, use every declaration only once, most importantly reduce amount of css files.
You can also optimize conversion rates.