Walking meditations are my favourite. I don't find it very easy to "sit" so this style of meditation suits me well. But even if you are great at seated meditations, practicing a walking meditation is useful both as a relief to seated meditation, and as an extension of seated meditation.
Walking meditation came by accident to me. During my 10 day silent Vipassana retreat a few years ago I spent all my in between meditating time walking. There wasn't a lot of space at the center, but there was a track around the small garden and myself and the other meditators could often be found, heads bowed, slowly circling the path. It wasn't long before I realised that this act wasn't a break from meditating, it was simply a different type of meditation.
Since that time, still having trouble maintaining a seated meditation practice, I often take to the beach for a slow stroll and some quiet time when I feel like I need to recenter.
A walking meditation is a great way to slow down and find your center. It can be done inside if you don't have space outside, but you should be alone to do it. My preferred places for a walking meditation are at the beach or in a beautiful garden. I would suggest walking somewhere familiar, or having a route planned out before you start so you can go within and not have to think about where you're going.
Start by bringing your awareness to your breath. Breath naturally, in through the nose and out through the nose.
Now bring your awareness to you stride. Slow your pace right down so that you are taking one step for every breath cycle - inhale as you place your heel on the ground, and exhale as you place the ball of your foot on the ground. Repeat on the other side. Then try one step on the inhalation and one step on the exhalation. Then switch back to normal walking pace and pay attention to the breath again.
Repeat this until you're ready to complete the meditation.