When optimizing css and javascript it can be done with a few clicks. The best way to optimize it, is by compressing and caching both.

Locate them at admin > configuration > development > performance. There you'll see two options:

1. Aggregate and compress css files.
2. Aggregate Javascript files

Check both items and viola, your site is optimized. Keep in mind that these settings should be on for the live site.

A few things to notice is that some of the modules does not work well with these settings on, like the administration menu. So turn them off when working on the dev site.