Every month The International Center for Reiki Training sends a monthly reminder for a World Peace Meditation if you are a subscriber (which is free). This meditation is very simple, and has many benefits. You can find the World Peace Meditation summary and instructions here:
The idea is that if many of us meditate, we create a healing wave of energy that travels the planet. The meditation requires only 15 minutes of your time, and you’ll personally feel the wave of energy.