Keeping your CSS files small and organized is very important, especially if you're going to spend any time editing your site in the future, (or if others are gonna be using the code i.e. clients).

Helpfully, there are a number of different techniques which can be utilized to aid organization and size of your CSS files in order to make them more streamline.
 
Having more streamlined CSS will save you time and stress in the long run so it's important to get it right.
 
Firstly, keeping a single stylesheet, normally named style.css, is a good place to start in the organization of your CSS. Having a single stylesheet for the majority (if not all) of your website keeps everything together in one place which makes the editing process more streamlined.
  1. Code in Style
  2. Organize by Location
  3. CSS Comments
  4. Avoid Duplication
See : http://goo.gl/Oi9xA