Several times Srila Prabhupada interrupted a lecture or a japa session to tell someone to “Sit properly.” Prabhupada writes: “First one must be able to sit properly, and then the mind and attention will become steady enough for practicing yoga.”
How we sit, stand or walk, or whether our eyes wander when chanting, affects our ability to concentrate and pray. Generally, the more your body moves around, or the more you look around while chanting, the more your mind will be distracted.
Remember, japa is meditation. The goal is to be absorbed in thinking of Kṛṣṇa. Slouching over, sight-seeing while taking a japa walk, looking around while sitting in one place, etc. will all affect your ability to concentrate.
Chanting is best done in the mode of goodness. I recommend that at least some of your rounds should be chanted sitting down, with your eyes focused or closed, and your rounds chanted softly. You will find that by doing this the mind will tend to be more calm. If you get antsy too quickly when you sit in one place, it is probably a sign that you need more sattva in your life – and especially more sattva in your chanting.
The reverse is also true. When you focus, when you pray while chanting, and when you are making an effort to be absorbed in the name, you will tend to automatically have the posture mentioned above. So when your eyes are wandering and your body is slouching or moving around a lot, become aware that you may be doing this as a result of already being distracted or disturbed.
You can also try chanting some rounds with your bead-bag over your heart as this may bring you into a more prayerful mood.
Write down the realizations you get this week by applying these practices to your japa.