Go out for a 15- to 20-minute walk. Does not matter where - the park, the city, the woods. Don't worry about the noise levels and activity levels in your walking environment. Just get walking.
As you walk, try not to think of anything at all. Just concentrate on your walk, your breath and all the sensory inputs coming in from the external world. But do not think. Do not try to process the sensory inputs with your mind. Don't give more than a passing thought to anything your senses notice or feel. Don't think of the past or the future. Don't think of what you will do after your walk. Don't even think of something 5 minutes into the future. Keep moving.
There are three main channels in which your thoughts can try to go astray - thoughts of the past or the present; thoughts of some other place or person who is not with you right there; judgments or opinions about things and people that are right there in front of you. Be aware of these channels. When your thoughts run along these channels, allow them to pass by like a leaf floating on a river. Don't try to resist any thoughts or follow them. Don't consciously try to add to, subtract from or multiply your thoughts.
Just keep walking. Be totally aware of your surroundings. Keep your mind clear of chatter. Be totally present in the here and now of your walk. Keep moving. Do this for 15 to 20 minutes every day.
Inspired by: The Power of Now by Eckhart Tolle