To make your store run smoothly and as fast as possible you should use JS & CSS merging. If you follow these instructions your Magento store front-end will be blazing fast.
1) Ensure that caching is enabled under System > Cache Management.
2) Go to System > Configuration.
|Advanced > Developer > CSS Settings||Merge CSS Files – Yes|
3) Install two Magento Connect extensions (free)
Fooman Speedster – View on Magento Connect
HTML Minification by Jemoon – View on Magento Connect
You’ll have to log in to Magento Connect, get the extension keys, and then log in to your Magento admin panel. Go to System > Magento Connect > Magento Connect Manager. After installation your HTML, CSS, and JS should automatically be minified.
Your theme now has combined and minified HTML/CSS/JS. If you want to take it one step further, you can enable Gzip Compression, Expires Headers, and remove your ETags. You can do this by editing your .htaccess file in the root Magento directory. For more information, view these Fast Division blog posts: