The core of the philosophy seems to be this: To have a good and meaningful life, you need to overcome your insatiability. Most people, at best, spend their lives in a long pursuit of happiness. So today's successful person writes out a list of desires, then starts chasing them down and satisfying the desires. The problem is that each desire, when satisfied, tends to be replaced by a new desire. So the person continues to chase. Yet after a lifetime of pursuit, the person ends up no more satisfied than he was at the beginning. Thus, he may end up wasting his life.
The solution, the Stoics realized, is to learn to want the things you already have, rather than wanting other things. The most interesting technique that will help you achieve this is Negative Visualization.
For example, suppose that you currently have a good working set of eyes. Imagine carefully what it would be like to live your life as a blind person. You would have to work very hard to rearrange your life to remain functional — learn braille, take special precautions when walking around town and when cooking eggs at home, etc. — but in the end, you could surely survive and even become happy again if you were blind. But now open your eyes. SURPRISE!! YOU HAVE THIS BONUS OF SIGHT!!!. Wow, you were already doing just fine in your blind life, but now you have working eyes too? What an incredible life – you are truly blessed with more than you even need.
It turns out that if you practice negative visualization on a regular basis, you learn to both appreciate your current life much more, and to be mentally prepared in the event of any changes in your life as well – loss of health, fortune, a loved one, etc. You have replaced negative emotions with satisfaction and even joy.