I walk a lot. I try to keep track of "how far"and meditate as I walk, by counting steps. Meditation is really just a trick: you're essentially letting go of conscious thought, to simply be -- aware. It's easier of course, if you're in a quiet place with no distractions, counting out your breaths in and out. The idea of slowly breathing to a count is the way you keep your mind empty: your brain likely can't do more than two things at once, so by counting out the timing of your breaths in and out, you're pulling your attention away from the conscious thought process. At some point you drift away from the counting, just as you allow thoughts that arise to drift away, rather than attending to them. You let your mind un-wander.
In walking, the counting serves somewhat the same purpose. You're not exactly out of it when meditating in motion; you're aware, but the sense of external vs internal allows you to be present without being caught up in it.
I know that 100 of my steps = 1 NYC up/downtown block; but I count anyway, to let go of the inner distractions. Like all physical activity, it can be hard to keep count for long, either because it's strenuous and you lose brain power after awhile; or it's complicated and there are distractions, like other players, or in my case, window displays, tourists, gunplay, what have you. So I use my fingers as a rudimentary abacus. Each finger on my left hand is a set of ten, each on my right is an entry in the 100s house.
At one point, I remember finding myself confused (not a rare occurrence) when I'd begin a new hundred: your natural instinct is to start with that first finger, as you count 1-10, but being both distracted and out of breath from walking fast, I would realize I'd hit the 20s but had tapped my third finger. Because I'm in a meditative state as I walk, I'm not really thinking about why. I'm not really thinking at all. But this time I thought of Roman numerals, and the abacus, and that this is the exact purpose of 0, to create a meaning to absence. In other words, if your fingers stand for tens, you must begin counting on your 0th finger. In meditation, you want to reach something like that-- an absence that is all presence. As in the tao, the emptiness is what makes the thing useful, like the hollow of a bowl, or the hole in the wagon wheel.
In zen Buddhism there is much reference to the concept of "beginner's mind" -- the idea of being open, approaching all with few preconceptions, willing to learn what is there to learn. You can't pour anything into a full vessel. It's hard for me to let go of my know-it-all attitude, although I realize my doing so must come as a relief to those who know me.
Accepting that I don't actually know much at all is a relief to me too. And research on the adult brain shows that neurogenesis occurs most when we are learning something new -- not when we've mastered it, but in the beginning, when we are working hardest and making mistakes. What if you could approach everything as if you were just starting out? Start on your 0th finger. And don't worry if you lose count.