There are some principles to consider during and after you write your CSS to help keep it tight and optimized. Optimization isn’t just minimizing file size — it’s also about being organized, clutter-free, and efficient. You’ll find that the more knowledge you have about optimal CSS practices, smaller file size will inevitably come as an direct result of their implementation. You may already be familiar with some of the principles mentioned below, but they are worth a review. Being familiar with this concepts will help you write optimized CSS code and make you a better all-around web designer.
Link: Smashing Magazine