Walking Power-Breath is a simple walking meditation that will increase the flow of oxygen to your brain. The benefits will be especially noticeable if you don't have much fresh air in your living space, or if the air outside is especially crisp.
To begin, find a place to take a leisurely walk outside. Don't exert yourself, and limit the amount of hills on your route. Next, breathe in so that your lungs are completely filled with air. Do this rhythmically to a count that is comfortable for you- I like the count of five. My counts generally last for two steps. Now, to the same rhythm of counting, exhale for a longer count (I use eight), so that your lungs are completely depressed of air. Repeat this for four repetitions, and then allow yourself to fall back into a normal pattern of breathing.
Repeat this exercise as many times as you want on your walk. You will find that you will gain increased stamina as your lungs achieve a greater capacity, and that your thinking will achieve greater clarity from the influx of oxygen reaching your brain.
At first it may be difficult to maintain a longer exhale count than your inhale count. Don't strain yourself, and take a break if you become light-headed. Eventually, this practice will become easier; your lungs will stretch and you will become more mindful of a balanced inhale and exhale.
This meditation is a very powerful way to clear your mind in the morning or evening.