I like to think about our minds as being the most valuable real estate property, and our thoughts as being the "tenants." To get into the best properties, potential tenants are usually screened, and then presented to a board before they get approved.
Our minds work a little differently. They allow thoughts to enter it without any type of screening. And they have the potential to effect us, for better or for worse.
The answer? Moving through the day mindfully, consciously aware of of our thoughts as they come and go. This way, there is no "good" or "bad" thoughts, rather there are thoughts that you chose to have there. They are welcome and wanted. They are like a good room-mate or neighbor. A pleasure to have around.
Today: Dedicate 5 minutes to paying attention to your thoughts, allowing them to come, and choosing which "tenants" you want to allow into your most valuable property, your mind. This can be done in a comfortable seated position, or as you move throughout your day.
Photograph via http://www.occupy.com/